Hi, jramauri,
I thought you might be able to use this:
Attached is a 2-layer sketch doc that allows you to either place reference or do a rough sketch on the first layer, and then go to a second layer with transparency to the first layer, so that a refined sketch can be done over the ref or rough sketch on the first layer.
Usage:
rough sketch on Layer 1 with RGB only, no ZAdd or material.
simple brush at size 2 or 3, with smooth stroke, circular alpha of any sort.
Switch to Layer 2 when done.
Transparency is preset (in material on layer) to medium.
Drag the material picker to get the material on Layer 2 selected, and change the transparency if desired.
If using Layer 2 to start a painting after finishing the sketch, hide or delete layer 1, or else set Layer 2 transparency to zero, or change the mat on Layer 2 to flat color (best choice for painting).
I like to get some brushes set up to improve workflow:
‘pencil’: Simple brush, 2 pixel, 20-30 RGB intensity (remember, no mat or ZAdd)
‘eraser’: Simple brush 10 pixel, high focal, 100 RGB intensity
‘smudger’: Smudge brush, 8 pixel, spray stroke with no color variation, dotted alpha, med intensity, low focal, no ZAdd
To use the ‘eraser’, set secondary color to same as ‘canvas’. Then just use ‘V’ key to swap between the ‘pencil’ color and the ‘eraser’ color. The only real difference between the pencil and the eraser is color, RGB intensity, and draw size. High focal helps eraser have sharp edges of course.
Using the ‘pencil’ and ‘canvas’ colors, I also have a quick erase method. ‘V’ to swap colors, and CNTL-F to fill the layer with the ‘canvas’ color. I just throw down some forms from imagination, and quickly throw away anything I don’t want to continue or don’t like. Then when I like the rough sketch, I go to the second layer and refine it.
Sword Dancer:
Quick sketch in using above ZDoc (I have a zcript of this session, but it’s 1.4MB zipped.) This is the final sketch from layer two. The layer 1 sketch was super-rough skribble to just get form, gesture, etc. Obviously, it was a little too rough. There’s plenty of proportion and anatomy errors in this one:
(Disclaimer: This post in no way endorses running with sharp implements, the sketching of scantily-clad humanoid females, quick-release skirts, sexual slavery, or violence against bunny ninjas. However, other ninjas, including the mutant varieties, are still fair game.) 
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