Prepare jello in seperate bowls according to package directions and let partially set.
Line a 9X13 pan (preferably glass or plastic - do not use a metal pan or it will discolour the graham crackers) with a layer of the crackers trimming to fit snuggly together into all corners.
Gently pour one of the flavours of partially set jello onto the bottom layer of crackers. Place a second layer of crackers on top and then add the other flavour. Sprinkle crushed graham crackers on the top and refrigerate until completely set.