Obviously the hamster is a mammal, but my little brother bought a hamster from a pet shop last year and he still isn't sure of it's sex. Mammals are easier to sex, but the teddy bear hamster won't let you put him on his belly and check.

Anyone know what to look for?
Can you tell by fur color?

Males are easy to tell. With all hamsters, you can see either nothing (female) or very obvious hamster balls (male). If you can't see anything , it's a female. It's super easy to tell if it's a male.

if its a boy it has a big butt that just hangs out trust me i have a boy european hamster who is a boy and heres another way to cheeck its sex but you must be careful and hold it in the right possision hold it by the neck like its mom does and wait till it stops movie and then part the hairs on its under side and see if there is 2 big balls and that is how a you find out what its sex is and by the way a teddy bear hamster is not a good choice to pick they are mean now a beginner hamster is a syan hamster hey are easy to take care of but a european hamster like my hamster socks is a better choice cause they are way calmer than any hamster