I am organizing an event where people can draw something on a plexiglas board with a transparent liquid and make their creation "come to life" by blowing coloured Holi powder on the glass where it will stick onto the written words.

Here's a video explaining it maybe a bit better:
My question is: What could that liquid be?? (in the example I am using lip balm, but that's not ideal, haha)

Conditions:
- it needs to be near to invisible when applying
- we need to be able to easily erase it with dry or moist towels
- it has to be biodegradable

By the way: Pure water doesn't work, because it's a) too runny and b) builds droplets and is therefore not evenly distributed.

Looking forward to your thoughts and ideas