I have the home-made cone thread holder so I asked my DH to add a bobbin holder. All he had to do was drill a little hole the size of a bamboo skewer, cut the skewer to length and glue it into the hole. Bam! instant bobbin tower.
I do fill 5 or 6 bobbins at a time with neutral colors for piecing. As others, I use neutrals or something that blends with my fabrics.