Implementing UI for that would be too bothersome. Have you tried to increase the Strength value in the Color scheme dialog (Style > Color > Color scheme > Tint)?
Yes I have, the problem is when the text overlaps the other regions that share the same color, which is exacerbated by having a dark background for the map as well as keeping the "Dark" color region dark. It's alright though, text can easily be added in post-editing so it's not a big deal