jlbadge,
The coloration changes after lower extremity surgery is very common. The venous and lymphatic systems rely on the contraction of the muscles to pump the fluids back in to the body's core.
So, if you are not using the muscles very much, there will be stasis of the venous blood in the foot/ankle, causing the redness and sometimes even a dusky appearance.
Also, with surgery, the veins and lymphatic channels are disrupted. Many of the small veins are cut and cauterized during the surgery. So, these have regrow, back into and through the surgery area. Thus there are less tubes to get the blood and fluids back into the body.
So, as you are able to use the limb more and more, and the veins reconstitute, the coloration will usually go back to normal. If you are allowed to do toe and ankle motion, that will help pump the old blood and edema back up the leg into the body. Of course, elevation of the foot, above the heart level, will also help pull the fluids into the body.
Good luck on your recovery and rehabilitation.