If you are in an angular-cli project, you can simply go to /node_modules/angular/material/core/theming/prebuilt and see your options for default themes.
Setting up your first Angular (2) Project Using Angular Material (2)
Tracy Lee | ladyleet

This seems that has changed, in my CLI project the path is node_modules/@angular/material/prebuilt-themes
Thanks for the article :)

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