this is the first thing i noticed upon testing the new schemes.
the solution is to create a new /color identifier that changes the color, then adds a new entry (or perhaps modifies the current scheme) in mirc.ini, then doing /color -l to load the new scheme (or modified scheme), then doing /color -s "scheme name".
however, that is just a workaround and it would definately be easier if mIRC would just update the current scheme with the new value automatically.