Unfortunately I don't think there's a way to adjust colour with luminosity-based restrictions like you can with hue- and saturation-based restrictions in the Color Editor tool.
However, there is one way to do this using curves, somewhat unintuitively. Basically you lift the shadow portion of the RGB curve, then decrease the shadow portion of the Luma curve by the same amount, like this:
Here's an example image:
It's a little clumsy and limited in scope, alas.
It's also sort of the opposite of what I normally do, which is to apply an S-curve to the RGB channel and the reverse of that to the Luma curve, resulting in more saturated shadows and highlights.