I'd like to surround black text with a white 1mm thick border in a Metapost label. Here is my code, which doesn't draw the border at all and which draws the text in white instead of black (I'm using mkiv and mkxl version 2023.09.26 18:19 on osx-arm6):

beginfig(1);
    % Define the text and colors
    string label_text;
    label_text = "Your Text";
    color text_color, border_color;
    text_color = black;
    border_color = white;
    % Draw the label with the specified colors
    label(textext(label_text) scaled 1.0, origin) withcolor text_color withpen pencircle scaled 1mm withcolor border_color;
endfig;