The British Empire used over 800,000 Indian soldiers in combat roles in the First World War (as well as over 400,000 non-combat personnel). Were these soldiers deployed to the most dangerous areas of the front so as to ensure white, British soldiers (or other Allies) would take less losses?
Well, I can't speak to the western front, but quite a lot of Indian soldiers were deployed on the Mesopotamian front which by all accounts I've come across was expected to be a cakewalk. As it happened the fighting there in the first couple years of the war ended up being quite horrific but that was equally true of [battles with the Ottomans that involved mostly white commonwealth troops] (https://en.wikipedia.org/wiki/Gallipoli_Campaign) and those that involved a huge mix of troops from across the empire including the home nations.
So again, without being able to comment on whether such a policy existed on the western front I would find it suspicious given the volume of Indian troops that were sent to fight on fronts that were thought to be easy pickings (even if they ultimately were not.)