[Engel]

Looks like heterochromia and absolutely nothing to worry about. My late Mania had one black and one red (I'll see if I have a photo).

Worth noting as you have a Syrian? (I mean as your personal ham). Dwarves have a scent gland on their stomach. If they're white I've found it can make the fur discoloured. Sometimes it can get blocked and a simple warm compress can help.

Just a few things to think about as you're rescuing and rehoming:
- keep all rescue hamsters in a different room to where your own hamsters are (to prevent the spread of disease).
- have a quarantine period of 2-3 weeks. This will allow for any illesses to crop up or any pregnancies to become apparent
- if you haven't already get virkon or F10. These are broad spectrum and depending on dilution, can kill most bacteria, viruses and fungi. (F10sc Can kill parvovirus and one I use myself.)

Regarding the eye changing colour. Could be ruby eyed. Appears almost black until it's properly in the light.