This change happened on patch 12.90.12195 (2022-07-19), one day after the update that introduced Gnomprona (12.90.12182, 2022-07-18).
In that patch, the sprites for male gnomes have been updated with smoother animations, and their colors (head/primary/secondary/detail) were swapped around - meaning that all male gnomes (monsters and NPCs) changed their colors noticeably. I couldn't find any other major changes within that patch.
I specifically asked about this change in this post that went unanswered, as I noticed it the day it happened. Later I asked a Tutor to follow up internally, and this was CIP's response:
This is indeed intended and is a fix for an old bug with the gnome outfit that was reported to us recently.
Nevertheless, thank you for forwarding this report. Could really have been one of the nasty bugs that always can come with a new update.