Ok, if you liked that minimum improvement here's the trick.
(1) Ideally choose a picture that has a clearly delineated outline or the difference of color is significantly diverse from the solid color of the background.
(2) You go to pixlr, paint.net
, gimp, photoshop, whatever, hell even paint 3d should do. You go to the magic wand tool and using the tolerance thingy you callibrate so it doesn't select any of the parts you want to preserve.
(3) Erase as much of the background as you can in one swoop. It'll look kinda shitty, but it's fine for now.
(4) Fill the background with a solid color layer.
(5) Extract the color for the new background from the borders that are still remaining. Usually the outer ones are fine.
(6) Finish retouching as much as you feel comfortable doing.
This process should not take more than 5-10minutes, and you'll have a relatively darker pape. If you want solid saturated darker color, you'll have to work a bit more as other anons have pointed out.
This one >>2203546
was like 2-3 minutes tops.