This is SO COOL!!!

How quickly can her species replace lost Colours? I assume they just gradually make more as they eat, getting bigger bit by bit with age? What of the mass left behind?

That's a question that would currently require a multi page essay to answer. For a super simplified answer: for a human massed Pondyolk, who is actively utilizing all of their Colours, they would likely need the same amount of food as a human and likely double or even triple the amount of water to maintain themselves while also creating new mass to grow larger and out pace the rate of losed mass. A Pondyolk's volume/mass, level of activity, and utilization of there Colours will greatly influence their intake.

Hopefully this gives an "okay" idea. I don't want to exposition dump any hard info. I'd rather show it off in future works. As it is not currently an exact science ^^;

Makes sense to me, thanks for sharing the little tidbit. Looking forward to seeing more of the exploration of Pondyolk in future works. Super neat!