I was playing in a new survival world in 14w17a and decided to make some grey stained glass. The grey dye created light grey stained glass. Confused, I made some light grey dye and used it in the crafting recipe to create grey stained glass.

To replicate:
1. Make grey dye, light grey dye, and glass.
2. Arrange glass in the staining recipe and place the grey dye in the center.
2a. This will create light grey stained glass, can hover over with the mouse to check.
3. Replace the grey dye with light grey dye.
3a. This will create grey stained glass.

Pictures included; Hope this isn't to lengthy.