A very do-able DIY inspired by COMME des GARCONS black label.
Take your piece, (I’m sure certain types of material will have its own unique effects) dip it in black dye and if you want more of a gradient look, hang it upside down and let nature do the rest.
This is pure brilliance. At first glance I thought they were cuffed bottoms showing the patterned lining material underneath, but taking a closer look, it appears as if the pants were dipped in plaid! When really they are plaid pants dyed in black, leaving the bottoms bare.