What about copying the map into Powerpoint, save as a jpeg and change the contrast?
I do that using IrfanView, as noted. (If you’re not familiar with it, IV is a very fast, light, but reasonably powerful image file viewer with some image enhancement options.) But when one starts with a white road on a beige background, there’s only so much one can do, esp. if one doesn’t want to use up all their toner on nearly “black” lakes and parks.