After I worked most of the folds and shadows in the 30% and 50% Greys in each tube, I continued by adding Cool Grey 90% to establish the very dark areas. At closer look, I realized the metal tubes weren't only in tones of cool grays but also had warm gray tones in them, thus I added warm grays. And its different because I often use only one or the other but this project lent itself to both cool and warm.
After establishing all the tones of gray, I then had lots of fun adding different reflected colors into the tubes. I see several golds and blues and some tones of red and brown. I found it easier to concentrate on completing one tube at a time. When they are all finished and I have laid in all the shadows, I will go back and complete the whole piece. This drawing is really fun and I am working on illustration board so I'm able to add many light layers of different pencils to the the subjects. I am also using Black in this piece which I normally don't use but it's definitely working in this piece to show strong darks and to depict the paint caps which are black.