Flickr Color Selectr
Flickr Color Selectr allows you to search for images on Flickr based on the primary color within the image.

Color Hunter
Color Hunter is a place to find and make color palettes created from images. When you search for color palettes by tag, ColorHunter.com searches Flickr.com via Flickr’s API for images labeled with the tag you entered. The thumbnails of the Flickr images are used to create a color palette.

Compfight
Uses Flickr’s API to search the database of photos and then feeds back the results as live clickable thumbnails.

Flickr Cover Flow
Cover flow slideshow web script like iTunes for your Flickr photos.

FlickrClient
Python interface for the Flickr API.

Flickr Color Picker
Using images from the Color Fields group, just click on a color, use the slider to adjust lightness and darkness, and it will show you photos with that color.