call method
Implementation
@override
Object call(Interpreter interpreter, List<Object?> arguments,
Map<Symbol, Object?> namedArguments) {
if (arguments.length < 4) {
throw "Argument must be at least 4.";
}
return Color.fromRGBO(arguments[0] as int, arguments[1] as int,
arguments[2] as int, arguments[3] as double);
}