I've been using <<stereotypes>> to categorize color combinations, but FontColor is applied differently to BorderColor and BackgroundColor.
box "Group 1"
participant "Alfa" as One <<Color1>>
box "Group 2"
participant "Beta" as Two <<Color2>>
participant "<font color = white>Omega" as Three <<Color2>>
In this case, participant Beta gets Black font, but should get White. Participant Omega applies it correctly, but the solution shouldn't be needed.
I didn't write it in this section of code, but "BackgroundColor<<Color2>> LightBlue" is still applied.