Colored coin is an interesting idea that leverages proven blockchain. IIRC, it would not require an alt-chain. But how can CC be used for open market trading and not just OTC transactions?
Basically, there is a way to do it

Basically, colored coins make trade secure, and so there is an easy way to automate such trade. (I.e. if it's secure anyway we don't need to hand-pick whom to trade with.
For a longer answer see here, second part particularly:
http://www.reddit.com/r/Bitcoin/comments/110scc/glbse_closes_frauds_investors_might_be_facing/c6ijun1