I think, I found by chance the reason for the wrong colour of the genitalia texture shown above: I have to activate the genitalia to draw on them. Blacksmith indicates the not active object(s) with greying them out. The clone brush takes the colour of the deactivated source object including the grey flavour. If I activate source and destination object, both objects appear in 'white' and the colour is matching.

If it's not a feature I do not understand, I consider it as an error, that BS uses the displayed (darker) colour for the clone brush instead of the original colour of the source.

The reason why I found out this is: I tried to create a tattoo over the pubic area so I used 'clear' maps. But clear here does not mean transparent, it means 'white'. I want to have it as ´transparent file to use as image layer over different textures. Is there a possibility to export a transparent PNG-file? The removal of the background with image editors has always some loosing of accuracy.