Veitchia Fading/Graying?

[Funkthulhu]

I have a couple juvenile palms in a large-ish (3 or 4 gallon? bottom watering reservoir) pot in my apartment.  North facing window, but it's a full patio door.  These guys have rarely seen full sun and have been slowly chugging away for about 7 years (since seeds were collected in 2012).  Now, the largest of the 3 in this pot has started thickening around the bottom (still narrower than my wrist) and its top-most frond almost touched my 8 foot ceiling before arcing over to hang a good 6-7 feet at its highest.  No changes to heat, light, water, or fertilizer in the last 3 years.

This winter it seems that the fronds are "fading".  Or that they're edging into a lighter green, to an almost grayish green, but still not on the edge of yellow.  I'm concerned because other than the color of the fronds, the plant looks really healthy and, as said above, the main trunk is starting to bulk up a bit.  Should I be worried? 

For reference, I believe this to be a Veitchia arecina, based on visual inspection of the mother tree, fruits collected and sprouted, and the look of the plant now.

[Funkthulhu]

I should add that it has overhead lights, some grow bulbs, about 12-16 hours per day. 

You can see it in the middle of this pile, the lighter almost yellow fronds: