Hi Susan. Yes, I see the luminosity definition as an unmarked marginal note that should go with the first occurrence of the word, in the instructions at the top of the page. I see nothing wrong with placing it after the instructions--in 7-5--since it applies to five questions which follow.
The color scale printed below the temperature label is associated with the temperature scale, so I would not remove it from its printed location. I see no benefit to making two diagrams since the data would be the same in both diagrams. This is going to be a busy drawing! Let me know if I'm not seeing something you are seeing.