Saturated color is rare in large planters for a practical reason: most large containers are molded plastic, and pigment mixed into plastic is what fades first. A sprayed finish behaves differently, which is why cobalt is available here at sizes where it usually is not.
Blue is a color to use deliberately. It has no natural partner in foliage, so it reads as an object rather than as a background, and one cobalt planter in a courtyard does more than five of them along a wall. It sits particularly well against white render, pale stone and weathered timber.
Jay Scotts' own comparison of materials is blunt about the alternative: over time, plastic can “fade, morph, and crack in extreme temperatures.” That is the failure mode a strong color exposes fastest, because there is further to fade. Related: green planters, round planters, patio planters and indoor planters. By size and shape: tall blue planters and large blue planters.