There's a great example here:
https://kb.novaordis.com/index.php/Gradle_Pass_Configuration_on_Command_Line
Which details that you can pass parameters and then provide a default in an ext variable like so:
gradle -Dmy_app.color=blue
and then reference in Gradle as:
ext {
color = System.getProperty("my_app.color", "red");
}
And then anywhere in your build script you can reference it as course anywhere you can reference it as project.ext.color
More tips here: https://kb.novaordis.com/index.php/Gradle_Variables_and_Properties