Hi SorceressGameLab, love your art!
The license for all my assets is an attribution license and can be read here: http://untiedgames.com/files/license.txt
In addition to the attribution requirement, the asset cannot be resold unless as part of a game or application product. (Since the GUI packs are not strictly game art I permit their use and sale as part of any type of program, not just game-like ones.)
So to answer your question: YES, you are allowed to recolor and modify it as you please for use in your products, which can be either for-profit or not. The license still applies to the modified assets.