d_value(`color`, `rgb(from rgb(20%, 40%, 60%, 80%) r g b / 20%)`, `rgba(51, 102, 153, 0.2)`);

    // Testing replacement with a number for r, g, b but percent for alpha.
    test_valid_value(`color`, `rgb(from rebeccapurple 25 g b / 25%)`, `rgba(25, 51, 153, 0.25)`);
    test_valid_value(`color`, `rgb(from rebeccapurple r 25 b / 25%)`, `rgba(102, 25, 153, 0.25)`);
    test_valid_value(`color`, `rgb(from rebeccapurple r g 25 / 25%)`, `rgba(102, 51, 25, 0.25)`);
    test_valid_value(`color`, `rgb(from rgb(20