Space invasion: Most Recently Used "History" color palette colors are wrong except . . .
GIMP-2.99 (and GIMP-2.10) "color history" palette colors (Most Recently Used colors) are only correct for images in the color space in which any given MRU color was created. So the user can't use a color in the color history in two different images unless both images are in the same color space as the color space in which the MRU entry was created.
So for example if the user paints a given shade of red onto an image, and that given shade of red is added to the Most Recently Used Color history, and if the user opens or creates a second image in a different RGB working space, the user can't retrieve and paint the same shade of red in the second image (at least not from the color history), because the same RGB values in different RGB working spaces, produce different colors.
One solution is to store the most recently used color history in one of the CIE color spaces such as LCh/Lab/XYZ/etc. Then the problem reduces to the standard "AnyRGB" problem of knowing what RGB color space the current image is in, when picking a most recently used color to use with the current image.