Definitely not nail polish.No nail polish is even completely safe for humans,even if they claim to be non-toxic
Acrylic paint is a bad idea as well since the ingredients are unknown and likely artificial(even if it claims to be non-toxic it might not actually be non-toxic).Use Elmer's glue or a DIY flour glue,but I'd avoid other glues.
As far as dyes go,make your own berry based or otherwise hamster safe food based dye.I wouldn't ever use anything artificial,but this way you can be sure that the dye is 100% safe and natural,so it will not be harmful in any way even over time
