These grips are CNC machined 7075 aluminum with an anodized finish. Both the front strap and back strap have polymer strips that mount on the pistol grip to fill the hand and offer better purchase than the aluminum alone provides. These polymer strips come in different sizes to best fit a range of people.
According to the company, the decision to add additional colors to the line came from customer demand for them. This is not surprising to me. Many people build their own AR style rifles, and having the ability to customize them is one of the main factors for many builders.
I know there are companies offering anodized uppers and lowers in a variety of colors like these from Thunder Guns. Being able to match component colors is a big deal for someone looking to make that special race gun or custom heirloom present for a good friend or family member.
Tyrant Designs sells the MOD grips for $120.90 each. That’s a bit more than what Magpul is getting for their MOE grip, but these offer a different design and construction that may appeal to you. The MOD weighs in at 4 ounces.