This year, bright colors are in. After all, black may be slimming, but in this race, red will let you stand out (and be easier to spot in a group photo).
Assuming no threatening weather (in which case I quickly start to add stuff), I have traditionally worn a long sleeve tech shirt. I pull up the sleeves before the start but can easily let them down once I hit treeline if the need arises.
Alternatively, some folks have taken to arm warmers usually sported by cyclist. They can then be easily removed and stashed in the back of the bike jersey pocket when no longer needed on the descent.
As for running vs bike jerseys, that is a matter of personal preference. Either way, I find that ones that are tighter fitting are better. This way it won't act like a parachute in the wind above treeline. While it may be ok when you have a tailwind, it can be a real drag when you have a headwind.
For shorts, I'll once again be sporting the two layer approach of my triathlon shorts under my running shorts. The tri shorts double as compression pants around my upper hamstring and quad, always nice. I'm a bit conservative in terms of my race day wear, so I'll have my running shorts on over them. This also gives me a pair of pockets to to stash a pair of gu's and the key to my car (with the key fob removed).
For the head I'll have my usual running cap on. It has a nice velcro'ed spot to stash a pair of gu's, so it does double duty. I don't like running up/down technical trails with sunglasses on, I find the sudden light to dark transitions leaves me momentarily blind which can result in a sudden impact with the trail when you trip over a rock. Others don't have the issue. To each his/her own.
One final thing for those making the round trip: Gloves. They don't need to be warm, they just need to help protect your hands when you take a digger. Keep them in your back pocket during the uphill and put them on when you get to the summit.
That's it for fashion week. We'll have a review of the best/worst dressed once the photos are online after this weekend's race. :-)