Admittedly a looooooong shot...
We're all taught that one of the prime objectives of typesetting is providing a uniform typeblock color (ie. the proportion of ink / no-ink on a page) as that is supposed to aid in reading and minimize distraction. That's the whole idea behind, for example, the
So I was thinking... why not take the definition of "color" a bit more textually: I'd like to change the color of a line depending on its tightness.
To put it another way: I'd like the actual color of the text to vary smoothly from pure 100% black for normal lines up to, say, 85% black for tight lines. This should be done automatically for every line in the typeblock (of course, we'd like to avoid abrupt changes in blackness, so a maximum of, say, 5% change in color should be enforced between consecutive lines).
I'm not sure this will be visually appealing, typographically sound or even doable, but felt like trying and stumbled on a brick wall... anyone care to share any ideas?
PDFLaTeX preferred, but non-exclusive.