If you wanna do that, just:
-unzip the file
-pick which color variant to edit (they have minor sprite differences)
-open theme.xml in notepad
-CTRL+F to replace every instance of the white (#e6d4be), black (#352b30), and red (#f6437b)
-open sheet.png, use the paint bucket tool with contingency turned off to replace the same UI colors, and that should be it ´∇｀