What do you mean? If you want a box to be a specific color, spawn and delete it until it is the color you want. But it seems to be random, as when I was forging a map with a friend yesterday, the boxes were different colors on my screen than they were on his.
Its not that simple, padres. If its like on Avalanche or Blackout then just place the boxes where you want them, save and quit. If they're the wrong colour, double tap A. Just pick it up and put it down in the same place, then save a quit again. Repeat until all the boxes are the right colour.