Or... You could keep the same amount of inventory, while offering half in one color, half in the other color...
I know it may sound easy on paper but it's a big no no for the purchasing dept.
basically the rule of purchasing (meaning how many units and variations of that unit a company orders of a product) is based on that item's availability, price and popularity.
because the Note Edge is the most expensive phone released in the US, and it's a pro phone and not a consumer one, like the S6, it also attracts only the tech-savvy added to that it was an experiment and was intended to be a very low volume product, it would not make sense from purchasing standpoint to make it available in more colors.
S6 gets all 4 colors, but the Edge just one. That makes sense.
Now it doesn't mean that every company is going to follow this rule, but VZW is no slouch and they are a success, because they know what they are doing.