I'm not sure yet whether I'll participate in this challenge, but anyway: here's a GIMP palette file I composed of the colors in the attached image. It might be easier to select colors from it instead of using the color picker every time.

CartoGuild-Lite-Challenge.zip

Installation for GIMP 2.x on WinXP: unzip the file and place it under .gimp-2.x/palettes/, found under the Documents and Settings/ folder.