And you didn’t even notice it was gone. Tsk. I didn’t either.
So anyway, you can now choose a colour from the image (click choose mask colour and then click on the image) and any samples that have that exact same colour will be studiously ignored.
I first put this is for making duotone type effects in conjunction with the shade solid pixel type and a few different colours of pens.
Use PNGs instead of jpegs, because jpegs often have lots of artefacts in them that are not the exact colour you want. Also bear in mind that it is the underlying colour that is checked for a match with the mask colour, not the averaged out brightness that appears in the density preview. Oh, and the mask colour is saved to the properties file too, and can be checked by looking at the info screen (press i).
Have a nice weekend!