The main use for the image-based color mode is obviously to pick colors but here is a very simple trick to use it as an actual drawing reference:
Pick any brush you like, switch to image-based color and load a picture:
You can rotate and place it as you want in your canvas and adjust the opacity of the displayed source picture.
And here is the trick: in the "Color Shifting" tab, check enable and push the value slider all the way to the left. That will simply make any picked color black:
Then just draw over your picture:
Once you're done, be sure to uncheck the "enable" box in the color shifting tab
or any color you use with that brush afterwards will be black too!