I made some Lime Bars yesterday. I used the Lemon Bar recipe that has worked so well for me and used limes instead of lemons. (Duh!) They are good! But, if I were to do it again, I might try Key Limes. The limes I bought at the store had no juice to speak of and I had to use a ½ cup of store bought lime juice. Also, I used the zest of 3 limes and 4 drops of green food coloring. I could have used 3 drops and had a better effect.
Next up on the list of Lemon Bar innovations will be the Orange Bar; naturally. Maybe 2 drops of red food coloring and 1 drop of yellow?