If, when you say glow ink sacs change brightness, you mean to the brighter color (eg §2 [green] -> §a [light green]), that's not what I've seen; the glow ink sac only seems to affect the "luminosity" of the text on the sign, a separate property not applicable to small sections, related to color, or given a code. If I misunderstood you, correct me.
The sign on the right is fully visible in the dark, as opposed to the sign on the left. Despite them having the same color codes (these two just had white dye applied), the right sign does have a different "luminosity" value.
[media]
I think the issue could still be identified in not being able to dye "black" signs, or just that the game doesn't make a distinction between plain black signs and color-coded signs. If I need to make a feedback post instead of a bug report I can; but I also view this as MCPE-117516 not really being fully fixed & maybe even a parity issue (see MCPE-129123 & duplicates).
cakeebot
If, when you say glow ink sacs change brightness, you mean to the brighter color (eg §2 [green] -> §a [light green]), that's not what I've seen; the glow ink sac only seems to affect the "luminosity" of the text on the sign, a separate property not applicable to small sections, related to color, or given a code. If I misunderstood you, correct me.
The sign on the right is fully visible in the dark, as opposed to the sign on the left. Despite them having the same color codes (these two just had white dye applied), the right sign does have a different "luminosity" value.
[media]I think the issue could still be identified in not being able to dye "black" signs, or just that the game doesn't make a distinction between plain black signs and color-coded signs. If I need to make a feedback post instead of a bug report I can; but I also view this as MCPE-117516 not really being fully fixed & maybe even a parity issue (see MCPE-129123 & duplicates).