I'm looking for a way to reproduce the effect I've tried to sketch in the image below with OpenGL ES 2.0.

The idea is to let a drop of color fall over a cube which get filled with a kind of 'pixelated' effect.

Could you figure out any feasible solution to achieve it?

Thanks for any hint!

DAN

*** EDIT WITH SOLUTION ***

Achieving good looking results with a procedural texture generated in real-time is quite hard. Here's a few screenshots taken from an implementation based on Nathan's idea, where the mask has been created by hand. Cheers!