Sign text is now darker than usual. It seems that by enabling signs to be dyed, the glowing feature was also accidentally introduced, which means that writing with bright text is currently impossible. It doesn't affect signs from previous versions, which means that it is an issue with the latest update, but technically it isn't a bug, as much as it is an accidental release of a feature. There is currently no glowing dye, but signs are now made to support it. I assume that it would be a simple fix, but this is in no means something which needs to be rushed.