1 Mike: Okay. We’ve made it to the Great Hall of Spheres. Without dying.
2 Eleven: Is there anything dangerous in this room in the D&D adventure?
3 Mike: Only what we bring with us.
4 Lucas: If that were really the case, we’d be doomed.

I decided to colour the entire Hall of Spheres from the original black and white line drawing included in the adventure module.

Friends suggested that it would look better if I replaced the stippling dots on the wall with a better wall texture. But after some discussion we decided to just leave it, to provide some more of that old school D&D artwork feel.

The colours of the "spheres" (actually 2-dimensional depictions on the wall) are canonical, according to the adventure description, by the way. But I coloured the rest of the wall according to my own choices.