This is a follow-up to an answer to my previous question, Why is this color so different in Texture Paint, and how would I change it?. That question had two parts, as indicated in the title. Both parts were answered by "Mr A". This question is a follow-up to his answer to the second part, How can I change this color in Texture Paint?
His answer told me that in the Image Editor, I should select the generated image texture that contains the color, then open its properties by typing "N", then go to the "Image" tab to find the color picker. I did all that, and I found the color field that should allow me to open the color picker, but that field and the rest of the "Image" tab are all greyed out:
Why is it greyed out and what do I need to do to activate it?

