When I get stuck or in grid lock on colors , I look at magazines ( most home dec) for color combinations I find interesting. I also look at what occurs naturally gardens, fall leaves,etc.
Many many times its a single fabric I fall in love with , and then coordinate with other fabrics, pulling the colors of the fabric into the project. Experiment with the bolts in the store .. stask them up and then stand back about 6 ft. the ones that don't belong will become apparent. A few things that help in picking the "stack" find a good mix of dark , light and medium coodinates. Having a quilt of all one canl read or appear to "lacking something".
Over time the confidence will come... and yes there will be some projects that will fall in the "What was I thinking" category ...