Well, there’s not much diversity in the books and movies we have nor much in hollywood in general, for that matter. Because white is treated as the default for characters of unspecified race in movies, Scamander will almost positively be cast as white even though there’s a great opportunity to have a non-white protagonist. I know that some folks in the HP fandom have felt very disappointed with the lack of diversity and representation, especially given the massive audience the Harry Potter franchise reaches. So, there’s that.
Also, Rolf Scamander, Newt’s grandson, was described as swarthy recently on pottermore, which points to him possibly being a character of color, which means that his grandfather could be a character of color. And that’s about as much as we have on Newt’s physical appearance, I think, but it should be taken into consideration.
Lastly—while I don’t think you meant it this way—I’d just like to remind folks that there are people of many different ethnicities, races, and skin colors in Britain, and that British certainly does not equal white.
On a related note, I really don’t think it will happen because the movie is set in the States in the 1920s, so making Scamander a person of color would probably mean discussing race in the context of the wixen world, something I’m not going to bet on happening given Rowling’s typical world-building.
That’s basically just my thoughts on the matter; sorry that it’s not very comprehensive.