In the list of commands from the Department of Provincial Administration (DOPA) to its subordinate offices I found one from November 18 titled การกำหนดสีสัญลักษณ์เพื่อเสริมสร้างภาพลักษณ์ของกรมการปกครอง (Definition of symbol colors for the Ministry of Interior). While the first pages of the PDF are scans, luckily the final pages contain real text and it was therefore possible to do a copy-and-paste to get a quick machine translation.
More interesting than the symbolism of these colors are the actual orders within this document. This color scheme is supposed to be used in documents like brochures as well as in the various websites. Interestingly as one example amphoe.com is mentioned, even though that site has disappeared even before that document was published. Not sure if this means the disappearance of that site was accidentally and for two months nobody at DOPA noticed it - well, would not be too much surprising if recalling the protecttheking website disaster.
Other places where this color scheme is supposed to be adopted is at district offices, so if a reader happens to see some newly painted fences, flower pots, or other items around the district offices in these colors I'd like to hear - being away from Thailand most of the year I can hardly notice these minor changes myself.