I've never thought about matching thread when piecing. If it's mostly dark fabrics, I'll go with a dark grey or black. If it's mostly light fabrics, I'll go with a cream or white. Then my go to thread is a medium grey thread.
For quilting as I don't consider myself an expert or if my tension will always be perfect, I'll use the same color thread on top and bottom. I tend to like seeing the patterns on the back side in the various colors anyway and I feel it adds character to the backside as well as the front side. Right now I'm using 4 different threads on this Alliitaire quilt top I'm custom quilting for my sister as she decided she wanted it once she saw it so many years ago when I made it. She's loving that she can see the various thread colors on the backside. Yes, I know this quilt top was made say 10 years ago and I'm just finally getting around to quilting it. THink it's the oldest UFO I have hanging around too so I am making headway on my UFOs.