I have found this issue on many multicolour prints on my X1C: When I paint an object in multiple colours in the slicer, using only the colour painting by height/layer option, the printer does not keep that whole layer that I selected in that single colour. Instead it keeps mixing in other filament colours, resulting in swapping colours for many layers that are supposed to be in that one single colour only! Besides the extra time every time a colour is changed in the AMS, it creates problems with almost empty rolls of filament not rewinding neatly on the spool, requiring manual retraction to allow the next colour to be loaded. That isn’t necessary if the slicer just did what I wanted, printing that whole layer in one colour!
How can I stop the slicer from putting other colours in a layer of the print that I only want to have printed in one colour?