Pick any brush you like, switch to image-based color and load a picture:
![Image](https://trello-attachments.s3.amazonaws.com/4ebcebb1f26b3ddb1e059c28/50bc7af70efb4885090021a4/b7960e65c712a4d1c8d9a2fb36b99910/catbasedcolor.jpg)
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:
![Image](https://trello-attachments.s3.amazonaws.com/4ebcebb1f26b3ddb1e059c28/50bc7af70efb4885090021a4/b3720ec2dd435719940ba1df000570f4/colorshiftvalue.jpg)
Then just draw over your picture:
![Image](https://trello-attachments.s3.amazonaws.com/4ebcebb1f26b3ddb1e059c28/50bc7af70efb4885090021a4/130b854146b1ee1f4eb636a7810b9e0e/catsketch.jpg)
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!