Here is one of the more unusual and fairly scarce Colt LT6720MPBLZ carbines.
The model code translates to LT6720 (rifle model) MP (Magpul) BLZ (Blaze camouflage).
The Colt AR-15 Resource
"A site dedicated to the history of the Colt AR-15 rifles, carbines and associated items"
The Colt AR-15 Resource 