What would make you say it will most likely be tan? I don't know much about Gigs, but am curious why it could lose that color?
Here's a photo of the nem at AC:
It has lost zoox since there isn't a brown overall tinge to the nem. I actually think the color of a slightly bleached gig looks BETTER than a healthy one, because the color of the nem is what is showing. Of course, the overall health of the nem is more important than color.
Once the zoox population comes back, the gig will turn brown. All gigs have a brown base color -- the purple, green, blue or iridescent "multi-color" are colors of the tips of the tentacles. I have yet to see a two-toned gigantea (not saying that they don't exist, I just haven't seen one in person).
Here's a gig I picked up from a LFS in January 2015:
It was almost completely bleached, but showed signs of a green center, like the photo of the gig at AC, but obviously not as pronounced.
Here's what it looks like today (you can also see the edge of a purple gig to the left and green gig behind it):
Here's a link to the old thread that shows it coloring back up:
http://www.reefcentral.com/forums/showthread.php?t=2474141
I still think the gig at AC will be a stunning specimen, though I'm a bit biased towards gigs! If it's given the proper conditions to thrive, it'll probably look like my tan gig.