I have a plan old Massachusetts Veteran license plate.
You can either leave it as it is with the flag symbol on them, or get a decal from the Department of Veteran's Services in Boston which has a decal from any of the 5 branches of service. It is simple, not overly done, and not one of those busy plates like ones with light houses, whales, kids, etc..,
Frankly, I think that any of these plates that say "proceeds go to......." are full of crap - but I have a natural distrust of politicians and beaurocrats so.....
As for the Colorado plate, I agree that the plain green and white plate looks best.