you're dithering is only giving your character a lot of unwanted texture, you are using so many colours so dithering in most areas wouldn't make a difference, I find it funny that people think dithering is like a necessity with pixel sigs, it's just not, only dither where needed to smoothen the transition between two colours or to purposely give texture to an object, you've just dithered everything and everywhere. Take your characters head for example, you've dithered were you could have been using the shades to define the shape of his nose, eyes, cheeks.. you definately need more contrast in your colours, and only dither after you think your shading is correct, and see if there are any areas you think 'need' it.
your colour choices are dark, and your lighter green tones don't compliment, it just looks like green velvet. your character's skin is very yellow, add some tones of red, blues in your shadowing, no nothing 'too' obvious.. I've said that and people have just chosen bright blue as a shadow. when you're selecting your shades, don't be scared to move your selector left or right slightly into other Hues, it'll make a hell of a lotta difference..
His chest muscles don't look right, and Im thinking his head is too small. otherwise this is a better quality than I've seen from others in the past (with runescape signatures). I see you're trying to get it too look more realistic, the only way to do that is to look at 'reality' look up reference pictures, get the muscles right, observe body positions, test colour combinations just anything to get it looking how you want it to look.
