I'm lucky back when I started 21 years ago. I got into building bows in a big way. And cut tons of OSAGE with those and all I've cut through the years I have and have had 100's. Have sold ,traded, gave away made dozens of OSAGE BOWS. At one time I had 233 staves.
Osage dose have oils and resins that has different affects on people. I found out long ago that when filing and sanding my my eyes puffy.
I not sure why OSAGE gets darker with age. But I LOVE THAT BURNT ORANGE LOOK. Osage doesn't stain well unless you use leather dye (alcohol based). I only seal my bows with bee's wax and let nature take it's course. Through the years I used everything to finish osage bows. What ever you use on OSAGE still gets dark with age.