...is there a DIY way to tell if what's currently in the car is the real DOT5 vs all the others?

I ask because way back when (so about 7-8 yrs. ago) when I finally finished restoring my coupe I was excited about using DOT5 primarily due to it's paint friendliness. It did help that DOT5 wouldn't absord water as well, and this being a non-ABS application I thought it made sense to go that way. But that was some years ago and while my build sheet says I put DOT5 in there, I honestly can't tell for sure (second quessing myself here given the years that have passed).

Well, I was looking at the MC the other day, the fluid in there seems sort of brownish to start off with (and I thought the DOT5 stuff was purple - I used Valvoline), and some of it dripped down on my re-finished power steering coupler. So I quickly went to wipe it clean (being used to the regular brake fluid impact on paint), and while it wiped nicely it looked like it dulled the finish...and that's when I started to think: "....Ummm...maybe that wasn't DOT5 I stuck in there to start off with????..."!!!

Sooo...that begs the question: is there a DIY test I can do at home to positively determine if this is a DOT5 fluid that's in there right now?

I thought of actually taking some of it out and putting on a spare finished part (car paint) to see what it'll do...but is that good enough of a test?

Thanks!