Feather colouring

How I coloured the feathers on A'mon Ch'akai, a Tzeentchian daemon.

This video was originally meant to contain how I painted the feathers themselves but XVidCap died on me at the worst possible time. The resulting mpeg-file was unreadable by Avidemux.

All painting done in GIMP, but it can be done in Photoshop too.
What I did in this was essentially create a layer on top of the one with the feathers in it. I switched it to Color-mode. I then tried figuring out a way to select only the feathers.
After that, I selected the Gradient tool, switched it to a rainbow-gradient and a counter-clockwise swirl. I applied this to the Color-layer.
I merged the two feather layers together and smudged the edges of the feathers to remove the hard border left by the selection.

DONE!

Music: Perennial Sophia by Therion.