Easiest would be just the same colors as already existing fluids since you already support nearly all vanilla and modded fluids already. Fluid names are just 'high-pressure-<liquid>'
Not as big a deal (as I don't train barrels) but as it's likely only an additional condition to add the same colors for the high pressure barrels. Names are just 'high-pressure-<liquid>-barrel' https://mods.factorio.com/mod/PressurizedBarrels
