You'd probably want to try that with lines that are just a shade darker than the surrounding colors, and keep the line as unbroken as possible so it reads as a solid line rather than random detail. Remember that when you're working on a pixel-level like this, a lot of detail has to be much more implied that anything else, and if you change just a couple pixels you can get a completely different effect. Right now, his chest just looks like it's covered in bolts, or buttons, or polka dots or something.