How light or dark a color is, independent of hue and saturation: the axis that remains when an image is reduced to grayscale.
Check the palette in grayscale; if the values are distinct, the layout survives any screen.
Value does the load-bearing work contrast gets credit for. Squint until the colors die: what remains is the composition, and if nothing remains, color was carrying everything, and will drop it on the first sunlit screen. Painters check value before hue; interfaces deserve the same discipline.