While time has shown that the average person can find a use for Facebook, Twitter, and Foursquare, I still find it very difficult to see how "another" social app... and a photo-sharing one at that... is going to draw the kind of crowd that would make this extremely high valuation reasonable.
I would agree that, based on numerous comments across the web, the only reason for such a high valuation is because of possible acquisition. But this article specifically mentions that the company is not interested in being acquired, so I guess I just don't "get it".
During the dot-com bubble, "eyeballs" were becoming as important a metric for companies as "revenue" or "profit". It seems to me (and others here) that we're seeing some of the same sentiment all over again.
The fact that Color will give me a 'dynamic social graph based on who I interact with frequently' does not make me want to sign up. Then again, I might not be their target market. I currently don't have much interest in sharing photos on the internet with strangers just because they are nearby.