France Maury #80 Tint Curiosity

Came across something, at first I thought aniline ink,
My next thought was it was dyed (Very well could be)
Now my thought has drifted towards it being on tinted paper (ya, not listed = silly)
So I'm looking for a suitable explanation to steer me correctly (yes it's old and use, so no telling what's happened to it in it's time)
Could be nothing and I'm ok with it :) I placed a note
thought I'd ask opinions?

I used a #97 to see what the tint looked like up close






(Easy enough…)

Then I looked for a stamp I knew was dyed






here's my curiosity….











I thought it interesting enough to look twice, again could be nothing but stained