[media]
Screenshot is taken using F2 (and using 4K display, without windows HDR mode)
Guide to reproduce:
Place signs with text and right-click them with dye. I used white on image. Text fades (does not disappear or change color) and darkens.
All signs should have same colored text as in X-axis, but in my opinion even X-axis should have brighter colours.
I've seen multiple bug reports on sign colors, but none using vanilla way to color signs with external modification or commands. This occurs without using any external mods nor commands.
This might not be a glitch, but rather an illusion.
There is an illusion involving 2 solid colored objects appearing to be a different color when the background is a darker or lighter shade. However, when comparing the solid objects together next to each other, they are in fact the same color.
This is the same thing here. The text color is not fading. The sign's surface shadow makes the text look like it's different because of the background of the sign. The text is the same color.