I don't know if its just Wii and Gamecube, but 99% of the game discs for these two systems never have more then 3 colors on them... Is it like this for all systems? I could've swore that the other consoles of this gen and last's gen have more colors on their discs... Am I imagining things?

I am assuming you mean the artwork on top not the physical disc colour.

It's just a cost cutting measure.
Nintendo Pinching pennies.

I actually prefer artwork on Wii games then for Example the 360, its simpler but better looking, here are some examples

http://www.teambadattitude.co.uk/art/wii/disc.htm

Few of them look really cool especially:
Umbrella Chronicles
Battalion Wars 2
Guitar Hero III
Mario Kart Wii
RE4 Wii
House of the Dead: overkill

Less is more

I don't really like the look of most Wii discs; I've always thought that, with the exception of a few good ones, most of them look a bit cheap, washed-out and plain. I'd love a bright, vivid disc but most of the time it's just a thinly-printed black and silver or one-colour design.

-_-

:P

Most of these games weren't published by Nintendo... thats the part I don't get...

Even if you don't publish through Nintendo, you still have to use the same disc-pressing facilities as they do, because the GameCube and Wii both use a proprietary optical media format. It's the fault of the facilities where the discs are printed more than Nintendo themselves; they just don't have the same kind of ink used for printing DVDs. It's closer to the old-style CD printing ink, in fact.

I like it better that way to be honest. Plus you don't look at the game disk, you put it in the machine and play it.

I like them, especially my BWii, Endless Ocean and RE4 disks.

The GC discs were a bit too small to get a decent design on, and ofen seem to have even more colour limits... so some of them can be dull, but tbh it doesn't make much difference.

For the most part it gives me a cheap feeling. But there are a few I like one in particular is SMG its just sexeh, but other hat that I prefer the PS3's disc art. Not that any of this is important as u should be playing the game not looking at the disc!