Finally received my bicycle tyre valve caps yesterday (the previous order were "lost in transit" so, progress was delayed somewhat.)
These are plain aluminium, but various colours are available - this could be useful if you wanted to allocate specific knobs to certain functions.
However, I opted for these ones - I think they match the overall style of the "control panel" of the layout.
The uncouplers and points are brass rod controlled, no electronics are involved.