In many cases the colour-production is dependent on certain definite conditions - temperature, presence of oxygen, nature of the food-medium, &c. Ewart's important discovery that some of these lipochrome pigments occlude oxygen, while others do not, may have bearings on the facultative anaerobism of these organisms.
In the encrusting type, which is found in a large proportion of the genera, the zooids are usually in a single layer, with their orifices facing away from the substratum; but in certain species the colony becomes multilaminar by the continued superposition of new zooids over the free surfaces of the older ones, whose orifices they naturally occlude.
They also can seriously occlude your vision in dark dance halls, not to mention reduce your peripheral vision, both of which could prove disastrous in a fast-paced couples dance.