The Conduit's disc is fully colored and that game is from June 2009. I'll check again in my collection to see if there is anything else.

I have Madworld, the disc art looks pretty sick, but it is not fully colloured.

Bought it for 10 bucks, lol. Its a good game nonetheless.

My first full-colour disc is probably Brawl, but I dunno...

Sonic Colors, appropriately enough

I think it started in 2009? But not sure I don't recall any 2006-2008 games being colored

My first was NMH2.  My most recent is S&P and DKCR.

Ok, I just checked my collection The first game I have with a fully coloured disc is The Conduit released on June 23th of 2009 in America. I also checked others and found that Boom Blox Bash Party released on May 29th DOESN´T have a full coloured disc.

So it happened in that period of time, some day of june 2009. Can somewhat check the disc colors of Tiger Woods PGA Tour 10 released on June 9th?, that game can be the first one, but I don't have it so I can't be sure.

I had never noticed this before.

Yeah, Conduit seems to be the earliest one I own as well.

I still remember SSX Tricky being the only Gamecube disc that had more than one colour (it had two :P).