re: Color matching dye stains

I use a Color Muse 2 to compare color differences and correct for them.  I went over this on LJ, but basically you're looking for differences and shifting your recipe to account for the difference.  Everyone knows green complements red and vice versa.  The others are blue and orange, and yellow and violet.  With those six colors you can take a color that's close to your target, like medium brown or Van Dyke Brown, and shift it to match the target.  Takes a lot of trial and error, but it can be done.  Aerosol toners are also a good way to do a final tweaking.

I should also point out that any color grabbing apps aren't going to be accurate enough because they're affected by the color balance of the light the measurement is made in.  Outdoors they will shift towards blue and indoors under incandescent or halogen light they'll shift red.  The Color Muse uses a calibrated light to compensate for that.