Cement grey is a neutral that behaves like a material rather than a color. It reads as mass, which is why it is specified so often on terraces and entrances where a planter is meant to feel built rather than placed.
The difference from actual cast concrete is weight, and it is not marginal. Jay Scotts put it simply in their own comparison of materials: fiberglass planters are “much easier than concrete to move around.” A large concrete trough is an installation that needs equipment and a decision you cannot revisit. The same shape in fiberglass is a delivery, and two people can usually reposition it before it is planted.
It is worth being precise about what this is: a fiberglass planter finished in a matte cement grey. It is not cast stone and we do not describe it as such. What it offers is the appearance, the non-porous shell that does not take up the water that expands on freezing, and a weight you can live with. Related: commercial planters, office planters and large outdoor planters. By size and shape: tall grey planters and large grey planters.