HSL

It depends. There is a new color scheme currently supported
by browsers called HSL:  hue, saturation, lightness. The actual color is
specified in degrees on the color wheel, below. The other two values
(percentages)are saturation and brightness. One would recommend using
this scheme in a situation where saturation  and lightness might change. So
that a red car, on a sunless day, but early in the day might be more realistically
rendered by dropping saturation but increasing lightness...

I first picked a pure red on the RGB scale and let the HSL self-adjust.
Then I played with the S and L values on the HSL and let the RGB
re-settle.