Unable to set PKInk color to black

For some reasons I am unable to set PKInk color to black.

It works with yellow, red, blue, …but black is just ignored and I get the stroke in white.

This is really weird and I don’t know why.

I tried by setting black to PKInkingTool and even by creating a stroke manually and set the PKInk color to black.

Do you have an idea? Thanks.