How exactly were non-white troops treated by European troops in WW1 and WW2?

In regards to African-American soldiers serving during World War I, black soldiers were received outrageously well by the French and British, long since used to black soldiers in their own armies. It would be the 369th Infantry that saw several of its soldiers receive the Croix de Guerre

The 369th became known at "The Harlem Hellfighters" or "The Men of Bronze" due to their reputation of never having lost a man captured, or trench or foot of ground lost to the enemy. It would also be the 369th that saw Private Henry Johnson who would be the first American and African-American soldier to earn the French Croix de Guerre and a Distinguished Service Medal when the Regiment was loaned to the French 161st Division.

Johnson earned his medal when "While on night sentry duty, May 15, 1918, Johnson and a fellow Soldier, Pvt. Needham Roberts, received a surprise attack by a German raiding party consisting of at least 12 soldiers...Johnson exposed himself to grave danger by advancing from his position to engage an enemy soldier in hand-to-hand combat. Wielding only a knife and being seriously wounded, Johnson continued fighting, took his Bolo knife and stabbed it through an enemy soldier's head."

Johnson would be posthumously awarded The Medal of Honor by President Obama. In addition to this, as many black musical units entered the Continent, Jazz and ragtime music spread across France, being picked up quickly by French civilians and military.

On the flip side of this respect, American soldiers did not treat people of color of any nationality well. French commanders were instructed not to salute or reward African-American troops in the presence of white troops. American soldiers would regularly get into fights with the numerous African auxiliaries that served in the British and French forces. Lentz-Smith tells "Back in France, white American soldiers shot and killed a black Brazilian sailor on the streets of Brest. Amidst calls by the Brazilian congress for an investigation, military police defended their actions by saying that the sailor struck them as dangerous. Although the American military ruled their actions justifiable, skeptics continued to speculate that “race hatred was the only motive for the killing.” (Lentz-Smith p.153)

Sources

Lentz-Smith Freedom Struggles: African Americans in World War I

Scott [The American Negro in the World War] (http://net.lib.byu.edu/estu/wwi/comment/scott/ScottTC.htm)

Ed. Wynn Cross the Water Blues: African American Music in Europe