According to Mollo:
'Native ranks adopted the tunic as early as 1856 and by 1861 all the native ranks were dressed in a turban which closely followed the undress tunic of the Bristish infantry.' p 135, The Indian Army; Boris Mollo, Blandford Press 1981
I suspect that the knickerbocker style trousers came in with the introduction of the shorter tunic around 1880. The leggings would date from the same time. Judging by depictions of of Bengali and Madrassi troops as well as what went before and came after trousers were probably blue. The again they could well have been white hot weather issue or even locally made items.
Minis? I don't know of any dedicated range for Indian Army for this specific period. Probably your best bet would be either the Foundry British from the China range with heads swapped for turbans or maybe Brits from Mutineer Miniatures with similar changes to headwear.