Yeah there's not much else you can use that's clear, unless you spend 100's of dollars a gallon on something like Fluorinert. But damn that would be cool. Thermal conductivity of mineral oil is much lower than water. But on the bright side, systems seem to stay stable at higher temps, because there are no hot spots

but technically I'm pretty sure you could submerge a computer in distilled water if you could totally seal the system from any metals entering the system, but that's probably impossible