I made the icing with wilton black gel, mixed it to a charcoal grey. I already iced the tiers and THEN tasted the darn stuff and its bitter. Can I fix it or do I have to scrap the whole thing?

it is always better to start with a chocolate frosting to get your deepness, then blacken it up with color. Americolor Super Black is the best for having no taste and getting dark. (though it might not be available if you don't have a cake store near you). In a pinch, i've used the Duff brand black gel color and found it not as good as Americolor, but a heck of a lot better than the Wilton. (it was only available in a four color box at Michaels).