I have only book knowledge about most of these options, but I'll share my
thoughts anyway. The first idea that comes to my mind is tinting your poly
with one of the many powdered tints available (there are water-based,
oil-based, and alcohol-based; I think you would use oil-based if your poly
uses paint thinner as its solvent). Another thing that comes to mind is to
make a pass over the floor with one of these tints before the poly (with a
base that is not compatible with your poly so it doesn't redissolve). Note
that if you intend to use a water-base, a pass beforehand with water to
raise the grain with a light sanding after dry is recommended in what I've
read. My third thought it that if you used a phenolic varnish, I believe it
will yellow over time to give it warmth, and should be plenty hard enough.
P.S. From what I've read, shellac wouldn't be hard enough; it would be a big
surprise to me to find out it has fared well in a high wear area.