[waynesonfire]

uhh.. or maybe just chemistry? you can fill the tank with urine if you want but YMMV.

[bregma]

That's fine for the magenta but what about the cyan, yellow, and black?

[spdustin]

You might be eating too many beets ;)

[dublin]

Methylene blue works both as a nootropic and a cyan urine ink source! (Dosing is often roughly "keep going until you pee blue all the time"...)