Whats the point of building an exchange for something specifically designed to avoid exchanges ?
Umm...how is this not an exchange?
I guess I need to provide some context... A centralized exchange like MPex both lists securities (including contracts, some statistics, etc) and provides the means of exchanging them, i.e. executes orders.
Decentralized exchange, like one based on colored coins, is supposed to provide an ability to trade without using one centralized service of some sort.
Basically, any trade with securities listed on MPex goes through MPex, and it depends on MPex. I.e. if MPex is down, you cannot trade. If MPex blocked your account, you cannot trade. If MPex knows who are you, it can report you to authorities. Etc.
Trade with colored coins can be completely person-to-person, e.g. you might meet somebody in person and send shares to their address and they'll give you cash. In a more realistic scenario people can use p2ptrade protocol which would allow to trade safely and anonymously. (Well, it is as anonymous as Bitcoin. I.e. probably not completely anonymous.)
But still, if somebody wants to trade using a centralized service of some sort, it's his right. It's just that people do not need rely on a centralized service.
OK, anyway. The way I see it, exchanges can still exist in 'colored coins' model, but their role is reduced to publishing listing information and whatnot. Exchange is an informational tool, it merely helps investors to find securities they might want.
There might be different exchanges. Perhaps some will enforce some quality standards for contracts and assets. (You know, like MPex lists few securities, but those have professionally composed contracts, some financial reporting standards and relatively high market cap.) It might provide additional services like charts, faster trading protocols and whatnot.
It is important to understand, however, that we are talking about OPTIONAL services.
Company can sell its shares without being listed on any exchange. (It can publish color definition on its own web site.) People can trade shares without relying on any particular service.
Exchanges are supposed to improve convenience for investors, and there is nothing wrong with it, it doesn't betray a goal of decentralization in any way.
In same way existence of bitpay and mtgox doesn't make Bitcoin any less decentralized.
