As someone said in the comments, maybe layered agar? (Or jello. Or colored hair gel. I'm thinking Dep.)

How to color it? And get that lovely bubbly effect?

I couldn't think what it reminded me of until Madamina said hair gel. The guy in the comments who said agar might be right, and that's also a type of "gel" that's not truly gelatin made from animal skin. Agar isedible and I think has cancer fighting and health properties and such, too, heh.

If you want it to be hard, of course, you could use a clear epoxy resin, either mixed with a bit of oil-based paint or just with a clear glaze of paint on the inside of the glass before filling with resin... but the newer, better resins don't bubble as much as the old used to.

It also reminds me a lot of that gel wax stuff people use in those "liquid" candles on which the wick floats.

I think you could do it with clear gel wax for candles. I've never made candles, but evidently you can dye gel wax as well as regular wax. It looks like the bubbles are a product of shaking or fast cooling.