How big do you want? Have you checked out Cabela's Orange Vest that has the pouch in the back, sides and inside also? I have had one for awhile now and use it quite often and it is also warm with the other clothing on too.
Brian i also have the Cabelas orange vest you are talking about.I have used it for about 6 or 7 years now.Its great for cold weather and or if your not packing to much weight.If you carry alot of weight it pulls down on your shoulders and causes back pain. I used it on an Elk hunt last year where i was going 4-5 miles in every day and with lunch water spotting scope and all my other gear by the end of the hunt i was miserable.I have retired it and purchased a Badlands 2200.Sorry this doesn't have anything to do with your post for a Orange pack.
other packs probably have this feature as well, but I use this one. It has a fold out orange flap that you can put over anything you carry under the outside straps.
LL Bean makes a few of their internal frame packs in orange or mostly orange, a number of the wildland firefighter pack makers make big lumbar packs in orange and finally, Mystery Ranch makes some of their packs in orange.