QBColor is not versatile enough to provide more than the
basic 16 colors, forget about using it.
OTOH, RGB can generate any possible 24 bit color. Check
Help for how to specify each of the primary color components
and play around with it on a test form.
The basic idea is that the higher a component's value is,
the brighter it will appear, so "light grey" will be a blend
of all three components at equal levels of brightness (with
0 for black and 255 for white). I like the pale gray I get
from RGB(224,224,224)