Hey drago! Those colors are defined by the user in the options window (and the possible options are in the file), but since it's a dynamic value there is possibly a /variable somewhere that you can query, but I don't know which one (maybe you'll find it on the / command list).
Alternatively I suggest that you attack something and simply query the color property of the health bar during each stage for the exact value in your case via UI script (e.g. via the ControlCenter in ProfitUI, that's what I have it for
).