Minecraft wiki entry for Sign, associated text: Oak sign with Glow Ink in the dark in 21w03a.
Difference in visibility of a lime text, from left to right, in a lit birch sign, unlit birch sign, lit dark oak sign, and unlit dark oak sign.
The comparison between glow text and non-glow text.
Signs being different shades depending on orientation.
All sixteen colors of glow text.