This has been vexing me a bit lately. Were the uniforms modified for service in India, or did they use the standard issue uniform?
I can see Company troops taking liberties with the uniform and I have used a mixture of figures to reflect a more casual look. Artillery with rolled sleeves from Eureka, AWI militia from Perry and Foundry and Crusader SYW British figures in more formal uniform. I had also thought that Royal troops may not have taken as many liberties. I had also assumed it was possible that regulation uniforms were cut from a lighter cloth.
Stuart Reid, in To The Ends Of The Earth, published by Partizan and in his Armies of The East India Company, published by Osprey, has the British troops in an early style topee, which was certainly issued later, but not as far as I could ascertain during the SYW. There are some other issues I have with the information in the first book, primarily having listed a unit serving in India when the regimental history indicates it was stationed in England at the time!
Having done quite a bit of reading on this lately, and having discussed with Cardinal Hawkwood, I have to say that there is very little evidence to indicate that Royal and East Indies Troops were issued with anything but regulation uniform, tricorne and all! Regulation items may have worn out and been replaced with gingham and other locally manufactured items, but it doesn't appear that these items were standard issue.
It appears that it was only in 1761 that it was realised one uniform would not do in all theatres. The first concession that troops in hot climates received was that a bladder was inserted between the hat and its lining.
I have also found reference to the fact that the Company was still using the heavy red jackets issued from England and not getting value for money as the recruits died too quickly due to disease!
Pictures of a SYW Swiss veteran in Company service indicate that even in 1772 the officer was still wearing his 1751 pattern uniform, but with increased lace denoting his advanced rank!
The three books above have probably been the most useful in researching this issue, although it is amazing how snippets of useful information pop up everywhere.
Lawson's Uniforms of the British Army was published between the 1940s and 1967. Carman's British Military Uniforms was published in 1957 and republished in 1968. Lawford's Britain's Army in India was published in 1978. Hawkwood recommended Lawson to me and it is a must if you have any interest in British uniforms and those of foreign troops in service.