Here are a few updated photos. Still not sure what color it is, and not sure if I'll ever definitively know because it's got different colors in different locations -- green on the tentacle tips and mouth, purplish tentacles in some places, tannish brown in others. It's not a plain tan gig, but is not an irredescent rainbow like others I've seen. Hopefully when it gets bigger its colors will pop more.
Here it is under mostly white light (Kessil A350 with the blue channel off, white channel at 100%):
And here it is under blue supplementation (Kessil A350 with the white channel at 100%, blue channel on at 75%):
Here's an FTS (the gig is on the far right, it shares the tank with a pair of wild percs, a bleached pink-based mag and green gig on the left, a bunch of softies and a ton of different macroalgaes):
Something unique about this gig compared to others that I had/have is that it has a lot of split tentacles. This accentuates its furry or shaggy appearance, especially since the tentacles themselves tend to stay narrow (as compared to other gigs which have tentacles that appear almost over inflated).