Newly discovered ore patches will have the correct color on the map. Previously mapped patches act very inconsistently; I don't know what causes them to actually update. Walking near them doesn't work. Radars near them doesn't work either. Most patches still have their old color after an hour or so of play, and some look like this:

Is there a way to force the entire map to update? Simply charting the chunk doesn't seem to work; I'm using the scanning radar mod (https://mods.factorio.com/mod/ScanningRadar) and it does NOT update the ore patchs map color when revealing chunks. So a full map refresh of some sort seems to be in order.