(Disclaimer: I am not guaranteeing anything with this process.  This description came from www.berryfit.com.)

If your chaps have faded or the color has gone out of style, you can dye them. Provided they are made of a good quality leather to begin with.

You cannot dye the finished side of a top grain leather as the finishes will prevent the dye from absorbing into the leather. You can however dye the suede side of top grain leather as well as chaps made from suede splits.

Use Rit liquid dyes because they are much easier to use than powdered dyes. The difference in price is negligible.

Changing some colors is easy. Like grey to black. But for some color changes it is best to strip the existing color first.

If you have never dyed chaps before, do something simple at first. Try freshening up a faded color or taking an old pair that's a lighter color such as sand or tan and changing them to navy or black.

When you are ready to dye the chaps, fill the washer with hot water. The hottest possible. Thoroughly shake the bottles of dye and pour them in. How much dye should you use? If changing the color, use four to six bottles depending on how deep you want the color. If you are just freshening up a color, just a couple of bottles should do. Mix the dye in the water thoroughly, then dip in a strip of old white sheet to check the color. This is especially important if you are dyeing the chaps to match a hat or shirt. Keep playing with the dyes until you reach the right intensity of color. Then put the chaps in.

If you're dyeing the chaps to a pastel color, let them agitate just a minute or two. Then pull them out and check the color. If it's not quite right, let them agitate another minute or two and check them again. As soon as the color is right, put the chaps in an empty bucket or tub while you drain the water. Then immediately refill the washer with rinse water and put the chaps back in. On the final rinse cycle, put in about a quart of pink fabric softener (optional). Let them dry by hanging them in the shade. After they dry, run them through the fluff cycle on the drier without heat to soften them and tug in all directions to stretch them out.

You have to do some guesstimating as to the color because when the chaps are wet, the color will appear darker than when they are dry. Also, a little of the dye will come out in the rinse water.

Dyeing for darker colors is easier. Agitate them for several minutes, then let them soak for a few minutes. If dyeing chaps black, you may even let them soak overnight. When you dye a darker color, be careful to rinse the chaps very thoroughly. Send them through the rinse cycle twice. Otherwise, the excess dye might rub off against clothing and/or the saddle.