This was fixed prior to the 4.5 release, it's on the plus45 page.. and there were several mailing list posts about it.
"
Save VGA text mode colour palette upon startup and restore it when switching consoles or when X11 exits."
Previously you could workaround this problem by setting a depth of 16 instead of 24... but Miod Vallat found a proper fix.
http://marc.info/?l=openbsd-cvs&m=123349965622593&w=2
http://www.openbsd.org/cgi-bin/cvswe...1=1.48;r2=1.47
http://www.openbsd.org/cgi-bin/cvswe...?r1=1.5;r2=1.4
http://www.openbsd.org/cgi-bin/cvswe...?r1=1.9;r2=1.8
Perhaps this bug still exists in the NetBSD 5 release?