The British appearance didn't really change much from their WW1 tropical rig right up to the outbreak of WW2. For the most part the same can be said for the Indians, though you seem to see Indian troops in shorts much more often between the wars than you did in WW1. By the late thirties the British and Indian armies' appearance begins to merge, with Indian troops dressing more like Tommies; in shorts, shirts and pullovers rather than the more traditional Indian Army getup.
There's an Osprey on the Indian Army 1914-47, and the Boris Mollo book "The Indian Army" is always to be recommended.