Can someone explain what is being said here in color publishing in the American Mathematical Monthly?
By default, color figures will appear in color online and black and white in print. If you want them to be in color in print, you need to pay the rates they indicate. All their papers appear both in print and online, it is not that you choose one or the other. They also advice on the required quality (resolution) of the figures (regardless of color) and ask that if you use the default option the colir figures are understandable and meaningful when rendered in black and white.

Other journals have an option for slightly different figures for color and black and white, which may make things easier sometimes (for instance, in black and white you use different kinds of shading as different "colors"). It doesn't hurt to ask if this is also an option here.