minor deviation in hue. It can also be a fully desaturated color of the base, as long as it is darker. Void may be pure black.
These colors would be acceptable for this base color. They are either a darker version of the base, or a darker and desaturated version of the base. The last color on the right shows a minor deviation in hue, and is slightly more yellow than the base itself. Notice that this small change is not overbearing.
These colors would be unacceptable for void. They are either lighter than the base coat or have too drastic a hue shift.