Minecraft wiki entry for Development_versions, associated text: The text on glowing signs now has an outline (MCPE-129123).
Black text on signs can be lit by using a glow ink sac (MCPE-128079).
Tooltips are now present when holding ink sac and glow ink sac when using a controller.
Ink sac and glow ink sac can no longer be used indefinitely on signs in Adventure mode.
Player can no longer dye text on signs in Adventure mode (MCPE-126489).