According to Sid Ryan's description, they do age and yellow a bit.
http://www.ebay.com/itm/Ruger-Bisley-Stag-Look-IP-Grips-VERY-NICE-/290606446064?pt=LH_DefaultDomain_0&hash=item43a97e75f0
I used Fiebing's Pro Oil Dye in Saddle Tan to add the brown touches and then seal with clear paint. I use a Q-tip and dot the color on so it will have subtle unevenness. They required only a little fitting which was done easily with file and sandpaper.