Photoshop pencil tool changed from black to grey while being used!

[Jannette31907324u5m9]

Pencil tool changed colour from black to grey while I was drawing. No settings had been changed. The colour selection panel says it's black. Clicking on 'black' doesn't change it. Foreground is black; background is white; opacity is 100%; fill is 100%.

[Jeff Arola]

Can you post a screenshot of the Pencil Tool settings in the tool options bar?

Is Auto Erase checked?