Not a bad piece, harking back to the days when GW actually made fun pieces for their armies.
Photo's a bit yellow cast, but the whole thing looks pretty decent. I'd have suggested that the Gobbo and the snots could have benefited from being slightly differing green tones. Perhaps amore acidy green for the gobbo and a softer green for the snots.
As for painting Black, lost of tips:-
1) Start by painting a mix of the Darkest Grey you have and Black.
Shadow with pure black, highlight with more grey to the black.
2) Add Bleached bone slowly to the black as a highlight, gives a worn & weathered feel to the black.
3) Add Darkest blue to the black as highlight, softens the highlight and helps create a more richer tone.
4) Buy Vallejo Model Colour Black Glaze, use as a thin intermediary wash helps slow down the transitions between highlights, without going overboard.
