Though bright colours are one of the most prominent characteristics of these postcards, they were sometimes produced without colour as well.
These uncoloured cards were almost certainly toned, either with selenium and/or sulfide, resulting in the warm, brownish tones and near total lack of deterioration.
One of the smaller publishing houses, Ketty, also experimented with tinting only the lips and cheeks of the figures in an otherwise uncoloured image:
From the early 1930s, uncoloured postcards often came with deckle-edges, which do not seem to have been used on coloured postcards.
The uncoloured cards were not otherwise treated differently– the publishing houses, settings, poses, and models are the same, and several couples sent both coloured and uncoloured cards. Indeed, one can find coloured and uncoloured versions of the same card (or, in this instance, photoshoot):
Note the deckle-edges on the uncoloured card.
In the mid-1930s, when this postcard style went out, the production of uncoloured cards was equaling or even exceeding that of tinted cards (dye-toning vanished entirely). These mid-30s uncoloured cards generally have more neutral tones, and are almost always printed on glossy paper.