I will tell you the Magpul OD green does not match the Alumahyde II or the Gunkote OD green. Magpul's color is darker and looks like they have more brown in it.
However, you can paint the Magpul products to match. I'm not sure about the rail covers, but the grips, stocks and mags all take it just fine. Apply just enough to cover, if you go heavy it gets gummy.
I actually bake my Alumahyde II in the oven @ 200 degrees for about 4-5 hours and it's hard as a rock. The polymer stuff came out great.
I would stay away from the close tolerance stuff, like threads, as Alumahyde goes on much thicker than Gunkote. I did my rails and my VFG was much harder to get on after.
It's very durable once fully cured.
Here's some pics for you, some of these do not represent the actual color, it was my camera settings. The ones that look dark green are what it looks like in person:
Magpul OD vs Alumahyde II OD:
Degrease VERY well, heat the parts and the paint up before you spray, and DON'T TOUCH THEM with your fingers until they are fully cured, oven or air.
Good luck!