I downloaded Interstate '76 today, and upon running the glide version AVG threw up a message that the file glide2x.dll was infected with "Win32/Heri". I couldn't find any record of anyone else coming across this, but I did see some references to this particular virus actually being a false positive. Does anyone know for sure if this is something to be worried about?

I'm getting the same message. Anyone?

Also, the colours in my game are all screwy (the road is rainbow coloured, as are buildings, and there is slight rainbow on the vehicle too.

There are several threads about this already, your best bet is to check out the sticky thread with the fanmade launcher which fixes these problems for most players:

http://www.gog.com/en/forum/interstate_76_arsenal/updated_new_i76_arsenal_launcher_with_automatic_workarounds_2_versions/page1

I don't know about the virus warning but I would guess it is a false positive.

999 out of a 1000 it is a false positive. All you need to do is search google for virus in x file and you will find out if it is a false positive or not. My Avira AV has never found a real virus but has annoyed me plenty with false positives. Many people have had their PCs completely hosed by false positives because they allowed the AV to quarantine the files automatically and they quarantined an OS system file or two. Which is stupidly the default setting in some AV progs.