To clarify by cannon fodder I mean were they given especially dangerous missions because they were considered more expendable?
http://www.1914-1918.net/faq.htm
How big was the British Army of 1914-1918? 8.7 million men served at some time
From the Indian Army and other 'coloured troops': 1,524,187
Total killed in action, plus died of wounds, disease or injury, plus missing presumed dead: 956,703
http://en.wikipedia.org/wiki/Indian_Army_during_World_War_I
74,187 Indian soldiers died during the war
956,703/8700000 = 11%
74,187/1,524,187 = 4.9%
If they were any such instances they were too few and far between to affect the larger scale of things.
This thing by Christian Koller suggests the French used Africans as shock troops. page 10
http://web.viu.ca/davies/H482.WWI/ColonialTroopsWWl.pdf
"We are going to offer civilisation to the Blacks. They will have to pay for that. I would prefer that ten Blacks are killed rather than one Frenchman – although I immensely respect those brave Blacks –, for I think that enough Frenchmen are killed anyway and that we should sacrifice as few as possible!"
Racism is obviously the issue here and the racism was very obvious. However it is up to debate whether they intended to use them as cannon fodder or use them as they would use infantry normally just in place of French troops.
May I ask where you got this idea from? How to approach this can depend on that.