Orange shellac,,even color it further w/alcohol based dye. Use it thinned out considerably. Full strength is too thick. Apply with a small pad like a cleaning patch.
A few quick coats to the rubber and then rub in some further highlight color in certain areas you want darker.
Lampblack is the standby but charcoal dust works well.
I still have a small container of copier toner from a long time ago. Black as black can be and fine as dust.
Rub into those areas and then go back over carefully with another light once over coat of the shellac or your fav stock finish works well too at this point.
Once dry, rub down to bring out high wear areas to your liking and leave the darker and the darkest as is.
You can singe the edges & surface with a torch carefully if you want the really aged blackened, cracked, sat in the closet look.
It helps to do it with linseed being brushed onto the surface, but it's touchy work and can go too far real quick. Then it just looks like an other rifle pad in need of replacement,,or worse.
I'd round the edges too. Looks a little California at the toe.
