How can I easily determine which colours were used in a specific psd file without having to dig through every layer using the colour picker tool?
In your case, just upload the photo to Color Explorer and it will analyze it and tell you what colors are used.
It can't import PSD, but you can just save it as a PNG or whatever and upload it.
There's also adobe kuler (sorry forgot about it!), just click the camera icon (create from an image), import the image, it will show you the colors, hit save and it will show you the color code.