Have you ever added white to a highlight over and over again, but your drawing or painting still doesn’t look bright enough?
The problem might not be your highlights. Your darks may not be dark enough.
This is one of the most common problems I see in artwork, especially with newer artists. It’s easy to be cautious with dark colors because once you make an area really dark, it can be harder to lighten it again. The result is that most of the painting or drawing ends up somewhere in way too light range.
Without enough dark values your highlights have nothing to contrast against.
Bright Highlights Need Dark Values
We see values in relation to the values around them. A white highlight surrounded by light gray won’t look that bright. Put that exact same white next to a much darker value and suddenly it appears dramatically brighter. You didn’t change the highlight at all. You changed the contrast in relation to the light and dark.
So when your highlights aren’t standing out, resist the urge to immediately add more white. You may already be using the lightest color available. Instead, look at the areas surrounding the highlight and ask yourself:
Are my darks actually dark enough?