I wore them once before realizing the knees were rather obviously faded.
For a while, I sadly thought about re-donating them or turning them into shorts, but then it occurred to me to search Google for ways to fix faded knees. Turns out there are all sorts of suggestions, including spraying them with dye—which I decided against because that would require me to open up my new packet of red fabric dye, and it would be quite a waste if unsuccessful. Another suggestion was to color them with crayons and then use an iron to set the pigment.
I gave that a try. Fortunately, I have an enormous box of crayons left over from my days as a camp counselor, containing every shade of red you can imagine.
After crayoning the fabric, it actually looked more faded than ever, but there was no turning back now!
At first, the pants turned disturbingly blotchy, but I remembered that many fabrics change color temporarily when they are hot, so I stayed calm and waited for the cloth to cool down.
When I was done, the faded spot was less noticeable than before.
Lessons learned: It is indeed possible to recolor a faded patch on fabric using a crayon and an iron (though I'm not sure how this holds up in the wash), as long as you use a darker crayon than the fabric you're trying to match!
Once my pants were a consistent color, I decided to get them to a more flattering fit, which basically just meant taking in the waist. The fastest and easiest no-sew way to do this is just to move the button. On these jeans, that would provide the added benefit of making the waistband look symmetrical, since the original location of the button was closer to one belt loop than to the other.
I had to consult an Internet tutorial for this task, too. I used the pliers method to remove the existing button, which got it off, but all the twisting and turning actually broke the rivet so it couldn't be reattached.
You simply poke the pointed end through the cloth (from behind, so it's pointing outward) where you want the center of the button to be.
Then grab your hammer and tap the backside of the rivet until the two pieces are securely fastened together.