This is part 2 of my Pixel Art Outlines Tutorial. If you haven’t read it yet, you should read that first!
Black outlines in pixel art can be very versatile, but sometimes they’re a bit overpowering or too retro feeling. The solution to this is coloring your outlines, though picking the right colors is very important.
The most basic technique is to use an outline that’s a darker shade of the object they’re outlining. For example, this green bush gets a dark green outline:
The color can be different on different parts of an object, for example this guys red shirt gets a dark red outline, but his pants get dark blue.
This is pretty easy to do on a light colored background, but if you have something darker, or with more variation, you have to be more careful about the colors that you pick.
The most important part of using colored outlines is maintaining contrast. The point of outlines is to further separate two objects to make it more clear to the viewer that they are separate entities. This means that an outline should always increase contrast, and never decrease it.