From your reference it looks like you have one liquid (isosurface) that might need to blend shader/color wise.
Kinda like the liquid is blue when it enters the glass, and turns red after it has collided with the glass, or comes in contact with other red particles.
I would approach that with a flip sim (liquid), and simply attribute transfer a color from the bottom of the glass onto the particles insided of a sopsolver, combined with an attribute transfer to transfer color from a red particle to the next red particle.
– -those are the basics.
If you wanted to go for actual proper flames, then I would not really work with only red and blue, but a gradation. Give each particle a “fuel” value and when a particle is ignited (by that “red” trigger), the fuel starts to reduce (vopsop in sopsolver), and it also starts to emit into a pyro volume (you might want to emit only fuel and emit temperature at the bottom of the glass to ignite the pyro). Then finally, when the particle's fuel is zero, you can remove it from the sim (blast it in the sopsolver).
Or… you could do everything in levelset (fluids), but in my opinion that might be harder to make sure the fire stays in the glass. If you are pooring fuel into a hot glass directly, most likely your pyro will ignite upwards and ignite the pooring stream above the glass.
By going down the particle route, you can better control when the state changes from liquid to fluid – and how fast and where exactly.
Should be a fun project!
If you are interested in digging deeper and figuring this stuff out on the microsolver level, have a look at Ahmad's work here:
http://nccastaff.bournemouth.ac.uk/jmacey/MastersProjects/MSc11/Ahmad/index.html [nccastaff.bournemouth.ac.uk]
Also you might want to search for that on odforce, he might have posted some hip files on that.
