Simple questions first-
Have you tried resetting ALL Brush sliders to default- Double-click on "Effect"
And set the Brush color to nothing- Double-click on "Color"
Overlays [O] are- Red, Green, White, Black (change with [Shift+O] - So not an overlay!
Yes, resetting the Brush settings should sort this out. But this must be done in the right sequence.
It is necessary to select the Brush tool and then immediately update the starting default settings - without having clicked on the image.
When you do subsequently click on the image, and thereafter, these changed settings will be the ones initially seen.
Once you've clicked in the image to place a new "pin" (or once you've clicked to activate an existing "pin") you can only then adjust the specifics of that particular instance.