Collapsing a joined graph causes graphs to change to darker FG color

Load 2 graphs, change colors of each and set to 'line', then join. Notice colors stay. Collapse joined graph, and see colors change to incorrect, darker colors. I assume that this is because 'collapse' changes the colors to a darker tone for annotations etc. However, for this use, the colors need to remain as they are set - so the user knows which graph line is which.