Historically, the Department of Defense has used an overall red blank adapter for the M16 series of rifles and overall yellow blank adapters for the M4 series of carbines. The yellow blank adapters are made to a higher strength specification due to the shorter barrel of the M4 creating higher gas pressures when blanks are fired. I wonder if this is an ‘early’ blank adapter for initial M4 carbines before the overall yellow color was adopted…The stamped words on the side of the blank adapter are:

Use M200 Blank
Cartridge With
M16-14.5 Inch
Barrel
Colt Firearms
Hartford, CT USA