I suppose I never documented that; just announced it in a Comment.
But it is simple enough: if you replace the root name of the image with a string that contains a percent sign, it uses that string, with the % replaced by the color prefix, as the URL in the HTML img tag, without paying attention to the specified graphicsDir or even graphicsType (if the string already specifies a file extension). The only requirement is that the 'external' images use the same color prefixes.
I suppose I never documented that; just announced it in a Comment.
But it is simple enough: if you replace the root name of the image with a string that contains a percent sign, it uses that string, with the % replaced by the color prefix, as the URL in the HTML img tag, without paying attention to the specified graphicsDir or even graphicsType (if the string already specifies a file extension). The only requirement is that the 'external' images use the same color prefixes.