You are trying to make a volcano and needs it to be gray what two food colorings do you need to make it the color gray?
The only way you can make it gray with food coloring is if the
substances you are making the volcano out of is white. You will
have to add black food coloring drop by drop until you have the
color gray you want. If you can't find black food coloring, mix
every color you have together then drip it in. All of the colors
mixed together will make black.