I've used the Google Maps Wizard to create the JSON object for the Retro style, pasted it into CustomStyle.Text, set the MapStyle to mstCustom and relaunched the map, and voila, the default style is shown.
Is there some more magic to be done with the JSON?
with WebGMaps do
begin
with MapOptions do
begin
CustomStyle.Text := '[{"elementType":"geometry","stylers":[{"color":"#ebe3cd"}]},' +
'{"elementType":"labels.text.fill","stylers":[{"color":"#523735"}]},' +
'{"elementType":"labels.text.stroke","stylers":[{"color":"#f5f1e6"}]},{"featureType":"administrative",' +
'"elementType":"geometry.stroke","stylers":[{"color":"#c9b2a6"}]},{"featureType":"administrative.land_parcel",' +
'"elementType":"geometry.stroke","stylers":[{"color":"#dcd2be"}]},{"featureType":"administrative.land_parcel",' +
'"elementType":"labels.text.fill","stylers":[{"color":"#ae9e90"}]},{"featureType":"landscape.natural",' +
'"elementType":"geometry","stylers":[{"color":"#dfd2ae"}]},{"featureType":"poi",' +
'"elementType":"geometry","stylers":[{"color":"#dfd2ae"}]},{"featureType":"poi",' +
'"elementType":"labels.text.fill","stylers":[{"color":"#93817c"}]},{"featureType":"poi.park",' +
'"elementType":"geometry.fill","stylers":[{"color":"#a5b076"}]},{"featureType":"poi.park",' +
'"elementType":"labels.text.fill","stylers":[{"color":"#447530"}]},{"featureType":"road",' +
'"elementType":"geometry","stylers":[{"color":"#f5f1e6"}]},{"featureType":"road.arterial",' +
'"elementType":"geometry","stylers":[{"color":"#fdfcf8"}]},{"featureType":"road.highway",' +
'"elementType":"geometry","stylers":[{"color":"#f8c967"}]},{"featureType":"road.highway",' +
'"elementType":"geometry.stroke","stylers":[{"color":"#e9bc62"}]},{"featureType":"road.highway.controlled_access",' +
'"elementType":"geometry","stylers":[{"color":"#e98d58"}]},{"featureType":"road.highway.controlled_access",' +
'"elementType":"geometry.stroke","stylers":[{"color":"#db8555"}]},{"featureType":"road.local",' +
'"elementType":"labels.text.fill","stylers":[{"color":"#806b63"}]},{"featureType":"transit.line",' +
'"elementType":"geometry","stylers":[{"color":"#dfd2ae"}]},{"featureType":"transit.line",' +
'"elementType":"labels.text.fill","stylers":[{"color":"#8f7d77"}]},{"featureType":"transit.line",' +
'"elementType":"labels.text.stroke","stylers":[{"color":"#ebe3cd"}]},{"featureType":"transit.station",' +
'"elementType":"geometry","stylers":[{"color":"#dfd2ae"}]},{"featureType":"water",' +
'"elementType":"geometry.fill","stylers":[{"color":"#b9d3c2"}]},{"featureType":"water",' +
'"elementType":"labels.text.fill","stylers":[{"color":"#92998d"}]}]';
MapStyle := mstCustom;
end;
Launch;
end;
begin
with MapOptions do
begin
CustomStyle.Text := '[{"elementType":"geometry","stylers":[{"color":"#ebe3cd"}]},' +
'{"elementType":"labels.text.fill","stylers":[{"color":"#523735"}]},' +
'{"elementType":"labels.text.stroke","stylers":[{"color":"#f5f1e6"}]},{"featureType":"administrative",' +
'"elementType":"geometry.stroke","stylers":[{"color":"#c9b2a6"}]},{"featureType":"administrative.land_parcel",' +
'"elementType":"geometry.stroke","stylers":[{"color":"#dcd2be"}]},{"featureType":"administrative.land_parcel",' +
'"elementType":"labels.text.fill","stylers":[{"color":"#ae9e90"}]},{"featureType":"landscape.natural",' +
'"elementType":"geometry","stylers":[{"color":"#dfd2ae"}]},{"featureType":"poi",' +
'"elementType":"geometry","stylers":[{"color":"#dfd2ae"}]},{"featureType":"poi",' +
'"elementType":"labels.text.fill","stylers":[{"color":"#93817c"}]},{"featureType":"poi.park",' +
'"elementType":"geometry.fill","stylers":[{"color":"#a5b076"}]},{"featureType":"poi.park",' +
'"elementType":"labels.text.fill","stylers":[{"color":"#447530"}]},{"featureType":"road",' +
'"elementType":"geometry","stylers":[{"color":"#f5f1e6"}]},{"featureType":"road.arterial",' +
'"elementType":"geometry","stylers":[{"color":"#fdfcf8"}]},{"featureType":"road.highway",' +
'"elementType":"geometry","stylers":[{"color":"#f8c967"}]},{"featureType":"road.highway",' +
'"elementType":"geometry.stroke","stylers":[{"color":"#e9bc62"}]},{"featureType":"road.highway.controlled_access",' +
'"elementType":"geometry","stylers":[{"color":"#e98d58"}]},{"featureType":"road.highway.controlled_access",' +
'"elementType":"geometry.stroke","stylers":[{"color":"#db8555"}]},{"featureType":"road.local",' +
'"elementType":"labels.text.fill","stylers":[{"color":"#806b63"}]},{"featureType":"transit.line",' +
'"elementType":"geometry","stylers":[{"color":"#dfd2ae"}]},{"featureType":"transit.line",' +
'"elementType":"labels.text.fill","stylers":[{"color":"#8f7d77"}]},{"featureType":"transit.line",' +
'"elementType":"labels.text.stroke","stylers":[{"color":"#ebe3cd"}]},{"featureType":"transit.station",' +
'"elementType":"geometry","stylers":[{"color":"#dfd2ae"}]},{"featureType":"water",' +
'"elementType":"geometry.fill","stylers":[{"color":"#b9d3c2"}]},{"featureType":"water",' +
'"elementType":"labels.text.fill","stylers":[{"color":"#92998d"}]}]';
MapStyle := mstCustom;
end;
Launch;
end;