This is pretty sweet, from DabbleDB:

Dabble DB
Then someone made a joke: why doesn’t Dabble pick colors automatically when customers upload a logo? Discussing it further, we decided we weren’t joking. Our graphic designer Luke was somewhat doubtful, but we thought it would be a cool feature, so we dove in. link »
The first thing we needed to do was figure out the logo’s background color. And that’s all the first version did, by using the corner pixels. link »
It turns out color theory has a way of measuring interestingness: saturation . So we pulled out an interesting color from the logo. link »
We turned again to color theory and realized we could use the border color’s luminance to decide whether black or white text was more suitable. link »
 - from Dabble DB Blog: White- (or green, or blue, or yellow) label Dabble via sharedcopy.com

Reminds me of something that Genometri presented at Geekout recently. This will be an interesting endeavor for color-challenged people like me.