Skydrol versus Clean Oil
Photo: G450 Remote Oil Filler, from Eddie's aircraft.
Photo: Skydrol (left) and clean engine oil right) in paper cups
The best way to tell the difference is to compare them. If you can fill a white paper cup to as little as an 1/8" you can tell. Skydrol is purple and clean oil is clear.
Photo: Skydrol (left) and clean engine oil right) on a sheet of paper
Even if you can't get that much of the suspect fluid, placing a drop on a sheet of white paper can help. In this photo we used plain printer paper, but if you have something that won't absorb the liquid, so much the better.