I am suggesting to be able to change the light color of any light source. It would also change the texture a bit. To dye a light source, you would simply throw dye on it. For example throwing Cactus Green on a block of Glowstone would turn the Glowstone green and turn its light color green. Black dye would do the opposite of give off light when thrown on a light source. Colored light would be great for decoration or Disco rooms.
I know you can change the beacon's beam color. But not the color of the other light it gives off.
Supported! This is a great idea because sometimes you just want to add a bit of red light to fully achieve that spooky feel, some grey light for a dark, foggy feel, or if you are bored you could just make a rainbow of colours! Sometimes I feel that Minecraft just needs more decorative elements.
Interesting suggestion, but I believe this was already achieved with Beacons. When you place stained glass atop a beacon's beam, it will change colour, and can even change tint if you add a variety of colours to it. I feel like we should keep this to Beacons for a while, but I do like this suggestion as well.