Did you try using the installers via Battle.net when you register your keys?

Older games also have colour issues on Vista and Win7 that were never patched properly, but for some reason the digital download versions don't have this issue.
Maybe they offer updated installers via Battle.net.

No, they are known to not work with modern Macs unfortunately. I did do my homework before settling on how I wanted to play my Blizzard games. Ultimately, running XP in Parallels is ideal and this also means I don't have issues with screwed up colors. This is also true for Age of Empires II which will run great for me on XP in a virtual machine. So, it's all good although the initial setup cost is there which isn't bad. I got Parallels on Amazon.com for 50 bucks and I already had an XP license from a long dead desktop which installed into it fine fortunately. Parallels is really great for playing older games. I don't even bother to run Win 7 in it although I could. I think it is better to just reboot for newer stuff (2007 to present) as it works just like on a regular PC that way.

I thought all the old Blizzard games that were released for Mac were for Mac OS and PPC?

If OS X still supported Rosetta, they would still work, however Rosetta was removed in Lion or Snow Leopard (I can't remember which).

Lion. I'm quite sure both Starcraft and Diablo 2 received Intel-native binaries though. (But apparently, as said above, they don't work with Mountain Lion - and I'd guess Lion as well, due to changes in the system).