SUMMARY Currently, it is only possible to select out of a few accent colours. It would be nice to be able to select the colour freely. For example, the current red is almost pink, but if someone prefers a darker red in companion with Breeze Dark, it isn't possible to select it. I don't know if it is easily possible, but it would be nice to have if it is.
The custom accent color selector is already implemented for Plasma 5.24: https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/1031
Well, then sorry for the noise and thanks for the feature :)