What is it with the dirty right side mosaic? Can you get some sense to it?

Clean the mosaic, first.

There is something scribbled in it. It is just so dark that you can't see it.

Is there any substance around that could give more light? Something phosphorous?

The cotton candy machine produces phosphor cotton candy.

Show the candy to the lamp and it glows! You can use it to light up the mosaic.

There was a mosaic piece laying around on the floor of the Concourse. Try it to the hole.

Maybe you could somehow stick it there. With something sweet and sticky.

Like a chewing gum?

Chew the chewing gum and stick it on the mosaic piece. Use the mosaic piece to the mosaic.

Yes, you have a skippable minigame. Try to fulfill the image. Left click picks the piece and right click rotates it.