I've already used a similar method for pieces like "Chaotic Hearts", but the class gave me ideas for how to expand on the technique, so I decided to complete the class project - which is, create 3-5 pieces of artwork by subtracting from a drawing.
The result was this 3-part art series, "Subtracting Night from Rainbows".
Maid of Stars and Rainbows
Forest of Weeping Jewels
Butterflies and SnowFlowers
Full Collection + Drawing Process
After that, I used the eraser to remove parts of the upper black layer, thus revealing the colors beneath in my chosen shapes.
In response to the course's recommendation, I also added layers, colors and shapes on top of the black layer, to add variety and interest. For example, the picture at the top of this post, "Maid of Stars and Rainbows", has stars added on top of her partly-erased black layer.
Because it was a quick experiment for an art class, I didn't draw it at full 8,000 by 8,000 resolution like I usually do for my print-on-demand pieces, so it isn't available on the full range of products, but you can get it on coffee mugs, journals, shower curtains and more in my Society6 and RedBubble stores.
In this case, I'd recommend RedBubble over S6, because it let me tile the image and thus add it to a wider variety of products and make it look better on them.
Here's what some of the available products look like: