6 Days Post-op and All Bruising is Faded to Yellow. However I Notice a Purple Bruise Under my Cast?

Bruising and swelling are almost always asymmetric.  Don't worry too much about uneven bruising.  Bruising is simply the product of red blood cells being broken down.  The skin on the bridge (dorsum) is very thin relative to say the skin over the nasal tip or cheek.  In order to "file" the bridge he had to lift the skin over it, and in so doing probably broke a few blood vessels (which is completely common and normal).  Ask your Dr. when you follow up if he recommends Arnica.

Bruising is the result of collection of blood cells under the skin after surgery.  Overtime, your body will break down the blood cells and cause the bruise to change colors from a dark blue/purple to a lighter purple, to orange, then yellow.  The process can occur at different rates in different locations on the face after a rhinoplasty.  The color differences you are explaining are completely normal, and you will have complete resolution of your bruising overtime. 

Yes, bruising happens after rhiinoplasty.  The skin is very thin over the dorsum of the nose for most peopel and can be very apparent.  Good luck with the splint removal tomorrow!