I use the bright colors for quilting and piece using beige (or cream), white (only with whites) or gray (with darker colors).

Right now I am using a light green on top and cream in the bobbin. I don't worry about the color because I use a fairly small stitch to piece.

I have been using Aurifil 50 wt 2600, a very light grey.

I use off white for lighter colours, and a steel grey for dark fabrics

for dark fabrics I use up left over bobbins, top and bottom, for lighter white or off white.