"Color by:" disappears after changing and going back to a layer. Proposed alternative approach

[LucaMarconato]

If we plot some annotations to a layer, then we change layer and we go back, the Color by: label disappears.

Also, I realized that a more ergonomic approach would be to remove the Color by: label and directly select the relative row in obs/rows etc that was used to make the coloring. But we could do it later.