Default [Q] Theme Help

I love customising the look of my phone but always find that a theme doesn't have quite what I am looking for.

If I wanted to edit a theme somone else made would it be a simple matter of unzipping the APK editing the png's (colourising them) and then zipping up the apk again?

Sorry about the numpty question, I browsed and searched the forum but it all seems to be quite chaotic and I am having trouble finding a specific answer.