Hi @GeorgSeifert, I am experimenting with a font containing color logo of a company. It works well, but I realized the bug described by @Bendy is still not corrected. If I build the color palette using CMYK sliders, the values are not stored in the .glyphs file. When you define your palette, close and open the file again, the color swatches are just black. (Solution: select RGB sliders first and then set your values.)
Related question: is there a way to store CMYK values in SVG fonts? Otherwise Black would be always converted into 4-color black which would be a big problem for proper reproduction of a logo with Black color value defined as 100% K.