Military uniform
The use of steel helmets was by now almost universal and a number of countries adopted their own designs moving away from the German, British, and French models of the First World War. The Italians, Soviets, Japanese, Swiss, Spanish and Portuguese were amongst these. Steel helmets, originally simply items of utilitarian protective clothing, were adopted as parade headdress by the French, German, Italian, and Soviet armies, amongst others, between the Wars.

Second World War: Uniforms of varying shades of khaki and grey were universal in the Second World War but the cut and outline appearance of the different armies still made identification in the field relatively straight forward. A Soviet soldier would, for example be distinguishable from his German opponent by his general outline, even in the fog of battle. British, American, Japanese and French uniforms still retained some distinctive features, even as they became more and more utilitarian in the course of the War.
The US Army discarded its First World War style field uniforms in 1941 in favour of a very plain and practical combat dress in a thin light brown wool shirt (sometimes with an olive green cast) and slightly darker trousers. This was worn in conjunction with a smart olive drab "Class A" dress uniform—which in many cases varied to a rich "chocolate" brown tunic worn with khaki trousers. There was a khaki version of the Class A dress uniform for summer wear. The war started with American combat troops wearing combat shoes with "spats" (a form of gaiters), replaced later in the war with 2-buckle combat boots.
By contrast, British soldiers, other than officers, had their 1938 battledress for all occasions.
In Germany the Nazi regime retained uniforms with many traditional features from Imperial Germany for its army uniforms, such as field grey cloth, marching boots (a taller version for officers), collar litzen (braiding) and breeches (for officers and NCOs); German Panzer (tank) troops had a special combat uniform made of black wool and German troops serving in tropical climates had uniforms in a shade of khaki. Later in the war, severe leather shortages led to the replacement of marching boots with ankle height shoes worn with gaiters (Gemäsch).

Imperial Japan used a light brown or khaki colour for most Imperial army uniforms — though there was also a green service dress tunic for officers. Footwear was reddish brown jack boots (restricted for wear only by officers), while soldiers wore shoes with leg wrappings puttees).
From 1935 to 1943, Soviet Army uniforms for all troops (except than tank troops) were an intermediate shade of brown; uniforms included a field uniform ("gymnasterka" shirt with collar tabs and a 2-button breast opening, belt, breeches, garrison cap, and boots), a service dress "kittel" tunic worn with breeches or trousers, and a dress uniform "mundir" tunic (worn with deep blue breeches). Soviet tank troops wore the gymnastyrka shirt, kittel (dress tunic) in a bluish grey (rather than brown) colour. In 1943, the Soviet Army began to re-adopt many Tsarist Army features, notably braided shoulder boards, which had previously been forbidden (since the founding of the Soviet Army) as a sign of an undesirable "social class" mentality. The reintroduction of these epaulettes in 1943 was a relatively inexpensive means of boosting Soviet troop morale. Once reintroduced to the Soviet Army, the use of shoulder boards was never rescinded and they remained part of the uniform until the dissolution of the Soviet Union. The distinct bluish grey colour for tankers was eliminated in 1943, from which point on all units of the Soviet Army wore brown.

Modern uniforms: Most military forces have developed several different uniform types, including combat dress, working dress, service or ordinary duty uniforms and (to a very limited extent) ceremonial full dress.

Camouflage: Today, all armies wear some form of camouflage uniforms for training and combat duty purposes. Armies facing service in different theatres may need several different camouflage uniforms.

Parade: Traditional coloured uniforms have long since given way to clothing more suited for actual combat in modern conditions. Bright colours are now usually reserved for wear by units having ceremonial functions, some bands and officers attending formal occasions. Elite units normally contrive to having some distinctive features. The United States Marine Corps are well known for their traditional midnight blue tunics and sky blue trousers (trimmed in red for NCO and above). These "dress blues" are worn for formal occasions such as the Marine Corps Birthday Ball in November. The British Household Cavalry and Foot Guards wear uniforms largely unchanged from 1914 for "public duties" i.e. ceremonial.
The military of many countries have adopted the economical expedient of smartening up combat uniforms for parade by adding medals, neck scarves and coloured berets to the terrain coloured camouflage uniforms intended for combat. As an interesting example of the combining of old and new features of uniform the French Spahis and the Spanish Regulares still wear the flowing cloaks, fezzes, turbans and sashes of the North African colonial regiments from which they are descended with modern khaki or camouflage clothing, on appropriate occasions.

By country: 

France: The battle dress of the French Armed Forces is the FÉLIN system combined with SPECTRA helmets. France has adopted a light beige dress uniform which is worn with coloured kepis, sashes, fringed epaulettes, fourragères and other traditional items on appropriate occasions. As an alternative parade dress, camouflage uniforms can be worn with the dress items noted above. The legionnaires of the Foreign Legion wear white kepis, blue sashes and green and red epaulettes as dress uniform, while the sappers wear the basic legionnaire uniform but with leather aprons and gloves. Troupes de marine wear blue and red kepis and yellow epaulettes. The Chasseurs Alpins wear a large beret, known as the "tarte" (the pie), and mountain outfits. The single remaining regiment of Spahis retains the white cloak and red sash of the days when this corps consisted of Algerian and Moroccan  cavalry. 
Sailors of the French Navy and Fusiliers marins wear a dress uniform dating from the 19th century with a distinctive red pompon on the round cap.
The infantry and cavalry of the Republican Guard retain their late 19th-century dress uniforms, as do the military cadets of Saint-Cyr and the École polytechnique. A dark blue/black evening dress is authorized for officers and individual branches or regiments may parade bands or "fanfares" in historic dress dating as far back as the Napoleonic period.

Germany: The German Army has retained a form of field grey for dress wear though of modern cut and worn with berets. Some senior officers still wear peaked caps. The collar braid stripes (Litzen), that distinguished regiments of the Prussian Guard prior to 1918, have become a general feature of modern German uniforms. The Mountain infantry troops retain a more traditional dress uniform. The Nationale Volksarmee of the former German Democratic Republic also maintained a stone grey uniform, following the Imperial German tradition. Both the West and East German militaries still retained Prussian-style dress uniform respectively, with the West abandoning the "Stiefelhosen" (bootcut trousers).
Until 1945 Waffenrock (English: service coat or tunic) – was the generic term for military uniform. This included dress uniforms, parade uniforms, and also epaulettes or shoulder boards with rank insignia, as well as uniform cuffs, badges and other insignia.

India: During the Indian Rebellion of 1857 the forces of the East India Company in India dyed their white summer tunics to neutral tones; initially a tan called khaki (from the Hindi word for "dusty"). This was a temporary measure which became standard in the Indian service in the 1880s. Only during the Second Boer War in 1902, did the entire British Army standardise on dun for Service Dress including the British Indian Army. The modern Indian Army uniform standardises on dun for khaki.
The Indian Army camouflage uniform consists of shirts, trousers, and cap of a synthetic material. Shirts are buttoned up with two chest pockets with buttoned flaps. Trousers have two pockets, two thigh box pockets, and a back pocket. The Indian Army Jungle camouflage dress features a jungle camouflage pattern and is designed for use in woodland environments. The Indian Army Desert camouflage, which features a desert camouflage pattern, is used by artillery and infantry posted in dusty, semi-desert, and desert areas of Rajasthan and its vicinity.
Parade dress for the modern Indian Army normally involve the addition of pagris (turbans), cravats and cummerbunds in regimental colours to olive green uniforms. Gurkha, Kumaoni, Naga, Garhwali and Assam units wear wide brimmed felt hats.

Indonesia: The Indonesian National Armed Forces have different types of uniforms worn by its personnel for certain occasions.