Interesting how perceptions can differ. More so when impressionism is the topic. I always see water as light blue to dark blue/dark green. But I think that's from being in the Great Lakes Region & seeing freshwater more. I seldom have seen one area of a Sea for long enough to judge well. Oh well...your rules I'm just trying to guess where each part of this is build might be leading to, if you like an idea, so be it. (great fun!)
I think the camera angle takes away from the lightness in colour, of the green. (Ooak?.Really...Neat! ), but what I see above is: A green field, and a "parade" filling it with animals and show folk, all in preparation for the setting of the circus's rings.
I see a dark railway roadbed, wide enough to share a stretch with the locals on their way to the fair too.
The marble..mar-bull..marrrrrble.....O.k,, I'm at a loss..Hey, it needs no "explanation"its pretty . Cur Rah Hee ; I.e., its nice enough to "stand alone".
A circus zebra being led across one square on occasionis a "must" though .
Are you Familiar with vintage American tv show "The Addams Family", and Gomez's layout? (search Youtube for "Gomez Addams trains") Though little to do with much here, and the lamps are fine on your corners, his corners are a good example of what I'd expect would work well also. One piece each corner, keeping the stone mostly unoccupied. If you get your signals near to the squares, the white stone will catch the red light when it's active. The stone gaining a red hue, and reflecting a pale, rosey light, up again as well.
(I just like playing with lighting. I had looked for a light splitting (rainbow) prism lamp (green glass) to show you too, but struck out finding it again... so far. .)
Oh, the glass top depots. If I could have only one accessory....Ya' know, I can't even believe they aren't still made (or the prices). I've even tried to figure a way to use one from HO and kids toy-Thomas sets. Colour me green with envy.
Tell Tom I said to think a bit about a "plain" drawer, with the face built as a "false apron/skirt". A hinged drop face, would hide things well when idle, make lack of pull hardware no big deal, and expose controls fully, or just partially without pulling on the whole drawer each time. A simple build up of deco shapes on the drawers face, appearing to be a portion of the frame between the legs, would work nicely. Fluting alternating panels, etc... optional..