Is it the anti-leak stuff that bakes onto the reservoir? I seem to have colourless power steering fluid in mine. There are still orange/red tide marks around the reservoir, so I'm assuming a previous owner changed it at some point. I even bought some fluid thinking mine was running low but after some fucking around, I discovered I couldn't see the level because the fluid was colourless.
I heard somewhere on YouTube you can get fluid that doesn't have the anti-leak additive, i'm assuming that's the colourless stuff I have in mine. I've no clue about it tho, it may deserve some investigation if the staining annoys you.