Thanks for the replies guys.

I tried changing shadows but it didn't seem to help unfortunately.

I did actually turn up my screen brightness and it seemed to help during daytime.

Night is still an issue however. I think the problem is that character models are subject to the same lighting effects as the game environment. This may sound pretty obvious and logical, however shouldn't characters be slightly more lit up than the rest of the game environment? It may not be realistic but it would help a lot considering they're the main things we look at.