As scc noted we are talking about this particular timeline, and the how and why of Western racism and it impact on the British occupation of India. While tied closely, race based slavery in the American colonies is only a tangent to the main idea here.
If it hadn't been quite as hardline as, lets say in Homeline, then we have more of a partnership among the British and Indian aristocracy. The British Raj can soon be considered a part of the West, much like Japan after WWII. My point is that British attitudes on race must have changed before Victoria or George IV, since by that time they were firmly entrenched.
Race, like religion, can be a hot-button topic, but can be used in a gaming situation to great effect IF you know your players and they KNOW you. I remember reading
Warlord of the Air when I was a kid, after reading a few of Moorcock's Elric books I thought I'd give this a try. I was shocked by the first section of the book. But that was used to great effect - I won't do spoilers just in case (although this IS an alternate history thread...) - but I would have dropped the book if I hadn't already thought Moorcock was a clever author and hoped that something was going to happen to change my mind.
Frankly if that had been in a game situation I don't know if I would have put up with it.