Question

How much control do I have regarding the styling of a google map?

Can I make it more closely resemble a site’s colour scheme or are we stuck with pastels?

Answer 1

Controls

There is a decent description of the process to override the set of builtin Controls. So you have total control over the UI elements overlaying the map.

Map Tiles

I don’t agree with the previous answers that you are out of luck if you want to change the images in the map itself.

The range of map types available give you a few options outside the pastel default map:

G_NORMAL_MAP, G_SATELLITE_MAP, G_HYBRID_MAP, G_PHYSICAL_MAP, G_MAPMAKER_NORMAL_MAP,
G_MAPMAKER_HYBRID_MAP, G_SATELLITE_3D_MAP, G_DEFAULT_MAP_TYPES, G_MAPMAKER_MAP_TYPES 

Obviously, this only works if you are willing to create the tiles, but Custom Tilesets are quite well supported by the Google Maps API and there a few good examples out there:

• World of Warcraft tileset
• Batmud tileset
• Tower of the Hand tilset

Update

Google recently announced support for Styled Maps in the Google Maps API. You can extensively customize the color scheme used by Google Maps. So you can customize the look of your mashup, without resorting to custom tilesets.