For Inverted drawings the most important thing is getting you colours right. There’s a very easy way to do this, if you open up settings on your phone go to General then Accessiblity and turn on invert, you can use your camera as a “filter”. You can use this to help select colours and also to help check progress while drawing.
For This Illustration i wanted White, Pink and Blue Colour variations, so Greens, Oranges and some reds were perfect.
Once i had my colours i got to work on the illustration and this is what it looked like finished:Not so pretty! now that the illustration was finished and photographed i Imported it to Photoshop. Went to image > Adjustments and clicked invert.