I need a sheetcake, half green (for grass) half black/gray (for sky) If i tint all of the frosting green, can I spray on half WIlton's black food spray to make the black/gray sky. I guess my question is what color will it be with black on top of green? I'm sure not many people have tried this but your input would be appreciated.
Sorry, but no, it will make a black-green sky, not gray. You can create a gray look by using the black spray on white buttercream very, very lightly, from a distance. It's no harder to ice a cake half and half with colors than it is to ice it as all one color. You just have to decide where to divide it.
Theresa 
Don't tint it all green. Only color the part u will need for grass and leave the rest white until u need to make it grey. This way u can add more green (for grass) if needed. I reccommend making extra (white) icing just in case..
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