Floor's white. Walls are black. Pits are dark blue.
I can see the use for each style to have a colour scheme that matches the style, though, so in Foundation walls would be a dark purple and pits would be a dark greyish brown, while in Iceworks walls would be a dark cyan and pits would be a dark grey. I'd suggest that for clarity the floor would stay white.
Also, I think that the stairs should be replaced by a gradient, from white to blue (to avoid confusion with blue doors).
I once went and put coloured filters over the minimaps to see if having the whole square red was easier to see. It actually impacts clarity a fair bit, which is bad. Maybe it'd be good to have a red filter instead of the floor being red, but the filter fades in and out so you can still see underneath it. The stairs could do the same thing, pulse from regular to a big, bright cyan.
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