my first question would be , are your pants 100% cotton ?.
next would be did you use green walnut hulls or dried ?
green hulls will dye just about anything even your hands but the color can be darker from my experience.
I would also agree with what gobbler and the others have said .
We used to have an old porcelain canning pot that my dad kept his walnut die in for traps .
What he would do is add paraffin to the boiling water . Once it was all liquefied, we would dip our traps .
This would take off the human sent and wax the trap all in one process.
When this mix cooled , the paraffin would then cool on the top of the liquid. Mom would then break it up and put it back in the shelf tell the next time . She would then add another hand full of green walnuts and just leave the pot sitting out side .
The thing would have in a few days , all kinds of stuff in it ., bugs , mould , you name it. As I recall it smelled to high heaven and got pretty thick . Something like real good coffee
But in no time if you dipped anything in it , that item even metal would come out almost black .
if you have some old iron laying around , it wont hirt to toss a peice of it in as well
What you need to do is soak your pants for a few days . Take them out and rinse them in cold water . If the color isn’t ark enough , soak them again . When you reach the depth of color you think want , go a little darker because when they dry the color can lighten up some ..
Now what we do is miz up a cold water , vinegar and salt mix and rinse the item in it . This sets the dye . Pretty good .
Now let the item drip dry . don’t wash it in a machine. Machines are designed to scrub cloths . You don’t want the item scrubbed, just let it dry naturally..
Later once dry you need to wash the item a couple times with a genital product like woolite . Do it by hand and the colors will last longer .
The other thing to keep in mind is natural dyes often fade over time with regular washing
