To make a polygon map accessible that displays some data attribute field: we "can not use color alone to convey information", we need to also include something else like text or hatching, or alternatively without those, I have seen that we can use the contrast between colors. It seems to me that looking at the contrast checkers, that we can only get 3 colors to have the required 3:1 contrast ratio. Am I interpreting this correctly? Is it impossible to have 4 colors that all have at least a 3:1 contrast ratio? If so what are the options for things that are categorical like land use types? It also seems like all the examples of accessible maps of color schemes online are not accessible when the colors are put in a contrast checker. Am I misunderstanding the tools or requirements? Or are the accessible colors, only accessible for a subset like red green color blindness?
