Linen/canvas on vintage strops

So on a lot of vintage strops the canvas/linen is brown. What is this from? Is it the dye from the strop seeping over, or is it lather or some form of strop paste? In any case, can one wash it somehow?
Thanks!

flax is naturally a tannish color and must be colored or bleached white.

Edit: Yes, the dye from the leather will seep into the linen, but this is much more pronounced on the leather-facing side of the linen.

I have taken vintage linens that had become lumpy & stained and I've washed them in cold water & Woolite. Let them dry flat with some weight (telephone books or what have you) on a flat surface. They have come out very nicely with no bumps and some if not all of the stains removed.

I'm in the process of doing the same thing. I have an old Vintage Scotch Shell that smells bad from cigarettes. The linen side has turned into one big filter. I took it off, pre treated it, and scrubbed it with scrub brush. Rined it, and let it hang in my Garage/workshop. It came out pretty good. One more wash cycle should do it, then it should be ready for some pastes or some other medium. I think that's what it will be best suited for. I could never bring myself to paste something new.....

I just hand wash it with a laundey soap any you would use for your clothes and a brush to scrub it in and the bad stuff out and hang or lay it flat like others have said mine took two washing this way to come completely white and clean