first mix and bake cake as required on the pakeage

in a small bowl get half of your icing and mix with 7 drops of red, 5 drops of blue and one drop of green food coloring (may need to add more of one color to get desired gray)

after cake cools apply gray icing and spread as desired.

then in other small bowl mix the other half of icing g with green food coloring (or any color you like). stir until you get the green you want

take grand crackers and break in fours (do not have to be even sizes unless that's how you want it) . place them around cake evenly spacing them.

finally put green mixing in a small plastic bag and push to one end of bag so that you can drizzle it over the cake. cut tip of bag and apply.

YOUR DONE!