The Geissele Super Modular Rail MK3 (SMR) was designed to be a cost effective option to their SMR MK1. The SMR MK3 is designed to fit the M4 Carbine and all mil-spec AR-15 variants. The SMR MK3 was designed to do a good job in meeting the ten design specifications for a good M4 weapon rail while being a cost effective alternative to the SMR MK1.
Geissele DDC, or Desert Dirt Color, refers to the variety of shades of desert terrain. Differing shades of DDC are desired on a military small arm to breakup the outline of the weapon.
These colors can vary from color seen in the picture of the product, and can also vary from each other when comparing one product to another product. So it is possible that your accessory rails will not match exactly to your rail.