It's free, and it tells you RGB color values from your camera roll – Pixel Picker - Image Color Picker Review

That was what I needed. I had some pictures where I wanted to check the RGB color values, I search the app store for "RGB colors," and I found this free app. I open the app, I pick a photo from my camera roll, I move the little pointer around to any spot in the photo, and the app and tells movie RGB value for that spot. I knocked off one star for not being able to copy the text of those numbers to my clipboard.
Review by Analytical Guy on Pixel Picker - Image Color Picker.