If you do cm2 = copy.copy(cm) and the original color map has been used at least once, then the copy will share a reference to self._lut (which is what is used to __call__ to map from values -> rgba). Any calls to set_over, set_under, or set_bad will be shared by all copies (as they update self._lut in place).
If you do
cm2 = copy.copy(cm)and the original color map has been used at least once, then the copy will share a reference toself._lut(which is what is used to__call__to map from values -> rgba). Any calls toset_over,set_under, orset_badwill be shared by all copies (as they updateself._lutin place).