I use the round doughnut like rubber bobbin holders.
I have one for each thread type and thread weight. I marked each bobbin holder with the thread type and size on the side of the center hole with a sharpie pen.
That way, I know what kind and what size of thread is on a bobbin. With my eyes and with having some threads in the same color only different sizes, I never could be sure what was on a bobbin. LOL...