[awqrre]

maybe he has a white cat and a black cat... but I would probably use RFID chips in their collar.

[kabdib]

That's what I'm trying first. RFID range is an issue, however. The electronics for this is easy, the problem is that I suck at carpentry.

The cats in question are pretty different (one black, one orange), so discrimination in visible light is easy. Not sure about IR yet.