They began the war in their famous blue uniforms, in 1915-16 they wore khaki shirts with their blue pants, and in 1917 a new completely khaki uniform was introduced.
One concession to concealment with the blue uniform was the abandonment of the red sash, and a cover for the fez. I think it started out light blue, but faded to white in the sun. You still see photos of askaris wearing their fezzes with no cover on, though.
There is a colour plate in the appropriate Osprey showing all three styles.