The rectangle exists to make a run, and white makes that run visible. Two troughs end to end read as one edge; four make a room divider that still feels light. Against dark brick, timber or glass a white line does something no other finish does, which is to separate the planting from the background entirely so the foliage reads as the subject.
Matte or gloss matters more here than on any other shape. A long flat white face with a gloss finish picks up a moving highlight along its length, and on a run of several planters that highlight lands differently on each one, so the line breaks into separate objects. Matte Bright White holds one even tone the whole way along. For anything repeated, matte is the specification.
The honest caution is maintenance. A white trough sits low enough that rain splashes soil up onto it, and white shows that more than any other finish. Both of ours clean with mild soap and water, and the manufacturer is explicit about what to avoid: no bleach, no power washing, no steel wool or abrasives.
