ok after a bit more experimentation, here's what I settled with.... set all colours to grey (or whatever colour you want the floor plans to be) in the first style, then re-colour everything you want in the following styles. This results in the floor plans appearing as a single block of colour.
var styles = [
{
featureType: "all",
stylers: [
{ color: "#505050" }
]
},
{
featureType: "road",
elementType: "geometry",
stylers: [
{ visibility: "simplified" },
{ color: '#505050' }
]
},
{
featureType: "all",
elementType: "labels",
stylers: [
{ visibility: "off" }
]
},
{
featureType: "administrative",
stylers: [
{ visibility: "off" }
]
},
{
featureType: "transit",
stylers: [
{ visibility: "off" }
]
},
{
featureType: "poi",
stylers: [
{ visibility: "off" }
]
},
{
featureType: "landscape",
stylers: [
{ color: '#FF0000' }
]
},
{
featureType: "landscape.man_made",
stylers: [
{ color: '#393939' }
]
},
{
featureType: "landscape.natural",
stylers: [
{ color: '#393939' }
]
},
{
featureType: "water",
stylers: [
{ color: '#252525' }
]
}
];