Just need to say this. If that image is your defense for making him grey, then you need to find a better image, or a better defense. There's, like, not a single tone of pure grey in that whole picture. Especially on mr. Cop himself. His armor plated self is full of warm copper tones from the surroundings. And even in stand-alone shots like
this... Oh, look, he's all sparkly blue! With interesting greenish darker tones.
That's what buloght meant. While I am a fan of using complete desaturation in some cases, it's VERY rare to find something that is just plain grey. Pretty much everything has some sort of color. I suggest you try doing some desaturated blue on your Robocop. The lineart is pretty good, by the way, looks like something you'd find on a SNES.