I think that they should implement stained glass. It would be crafted with normal glass, and the color dye of your choosing. Then the same way you make glass panes you can make stained glass panes. Stained glass would alter the color of the lighting in the room it is in. The reason I think this is a good idea is because it would improve many builds people have made, it wouldn't change the feel of Minecraft like some other ideas, and I feel like many people would appreciate this being introduced.

p.s. Sorry I just quickly colored in one side of the glass block. =)