As someone in the same position as the OP, first thanks for the ideas, it is a useful post. But I am a little surprised about advising against colour theory (the only of those suggestions that I actually know anything about).

Sure no need to go into depth, but there are plenty of short easily manageable resources for getting the basics. Before I read a blog post about colour theory I had no idea the concepts even existed. Now I'll use an online tool to help me select colours that will work better together. The effort required is basically a bit of google, and less than an hours reading.