test_valid_value(`color`, `rgb(from rgb(20%, 40%, 60%, 80%) 0 g b / alpha)`, `rgba(0, 102, 153, 0.8)`);
    test_valid_value(`color`, `rgb(from rgb(20%, 40%, 60%, 80%) r 0 b / alpha)`, `rgba(51, 0, 153, 0.8)`);
    test_valid_value(`color`, `rgb(from rgb(20%, 40%, 60%, 80%) r g 0 / alpha)`, `rgba(51, 102, 0, 0.8)`);
    test_valid_value(`color`, `rgb(from rgb(20%, 40%, 60%, 80%) r g b / 0)`, `rgba(51, 102, 153, 0)`);

    // Testing replacement with a number.
    test_valid_value(`color`, `rgb(from rebeccap