In the new version of Paper released last week, you mix colors with your fingers, like it’s paint—only somehow more beautiful. This one magical feature burned a year of development time, resurrected the work of two dead German scientists, and got Apple’s attention.
To model colorant mixing you need to use subtractive color models. Adding a blue paint and a yellow paint together result in a paint that subtracts light in both the areas that the individual paints subtract in and relate to their concentrations and relative proportions—an over-simplification but conceptually true. None of the color representations referred to in the article (RGB, HVS, LAB, LUV, …) are subtractive, which is why the “yellow plus blue don’t give me green” issue arises—linearly mixing RGBs was never going to work as it’s not meant to :) Even taking a simple CMYK (e.g. a standard one like ISO Coated v2) space would have already solved this one issue alone…
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