That didn't go to plan. You just wanted to help your friend the artist redecorate. In the process you mananged to make an ugly notch in their favorite table, scratch their wall when moving said table round a corner and as only now you notice to knock over a jar of ink sat on the same table which as if to mock you has found its way over the table's surface to the notch and down through the notch in a neat focused beam onto some concepts your friend had been careless enough to let lie on the floor.
Your friend is a person of superhuman patience and will let you get away with murder but spoiling their sketches is another matter. You my friend are in hot water. Luckily for you I happen to have a magic eraser on me that can remove any kind of ink. It will remember the first color you touch and then continue to remove all ink of the same color but none of any other color. Magic, wouldn't you agree?
What? You are kidding me! You have forgotten which color? And no ink left in the jar or on the table? Well, I don't care. I'm a geenie, not a charity. Here is your magic eraser, please sign the receipt here, and good day to you. One final word of advice, use your brain, it can't possibly be worse than your hands!
Will you be invited to your friends next opening event? It's in your hands---which, all things considered, doesn't bode too well...
Problem was given to me at a party (yes, that kind of party). Exact source untrackdownable I'm afraid.
The stacking of colors (which line crosses over which other) on that doodle, I mean concept art, is not a clue. It should be obvious from the overall quality of the pictures that such attention to detail is not at my diposal. That said, there is information in that picture.
Generally: Read the pictures as schematics. They contain information but whatever fine detail subtleties you may find are unlikely to be intentional simply because I wouldn't be capable.
As the best approaches so far have come from non mathsy people: If you are one of those and nonetheless want to have a shot:
you only need a single theorem, possibly multiple times: https://en.wikipedia.org/wiki/Inscribed_angle