SUPPORT:
You have mentioned that support is really hard(reason i dont remember)but i am thinking of giving each particle a text id of the preset used ex:preset = "water"
You dont change the general liquids anymore but instead you change the presets as they now work as liquid types.The con is that it will consume more random acces memory but you could make multiliquid a hard option(you have to confirm to change like particle limit) so lower perfomance pcs could run it better.

Mxing:Natural color mixing - get every particle type in the line that the pixel covers and average them.It may be consuming tho so its probably should be also optional.

It could break some mod support but as GW2 is pretty new devs would fix it really quick.