I use the same thread in bobbin and on the top.. I also use 50wt thread, found out a couple of years ago it is better to piece with...Who knew

For piecing, I use prewound bobbins so the top and bottom threads are generally different. For quilting, if I am using regular thread, the top and bobbin match, but if I use heavy thread or metallic I color match but use a thin cotton. For garment sewing, I match.

I'm a "collector"...I always buy thread at garage sales and anywhere else I can find it cheap. I use it to piece, and don't care if bobbin and top are different colors, it never shows. I save my good thread for quilting, where it will show. The colors that I choose for top and bobbin depend on the quilt and quilting I plan to do...if I want the quilting on the back to pop and create a reversible quilt, or if I want it to blend and be hidden.

I often use the same thread for piecing and quilting and only adjust the color. For piecing, I try to stay with neutrals but sometimes I will use up leftover colors in the bobbin.

Sometimes I use a thicker thread in the top and a thinner one in the bobbin. The color depends on the project.
I also like monofilament in the top with a 50 weight cotton in the bobbin.

Honestly, there are some spools I don't know what they are. I still use them.