I am about to flush the clutch fluid, but mine looks really weird:
I am having clutch issues, have had since I bought it.
DMF has is no longer performing but the clutch bite point is soggy and long.
Car only done 60k.
It might jut be old, and has picked up debris from inside the system. If you flush and change it, and it stays clean then all is good!
Scientists have been searching for dark matter for a long time, so fair play in beating them to it.
I have a small amount of the 'dark matter' in my clutch reservoir and I've seen it before on a few other cars.
I seem to remember reading, is the rubber in the seals and the cap breaking down over time? Nothing to worry about if the system is functioning normally.
The over all colour however, is way past what I would consider normal. Definitely worth bleeding the system like you planned.
Top tip: Remove as much of the old fluid/matter from the reservoir as possible, using something like a syringe.
Saves flushing it through the system.