Wit darkening in secondary.. but why?

To save research and shopping time, I've been brewing Brewer's Best kits from my lhbs. My current batch is their wit, which was looking mighty fine, cloudy and orangey in the primary.

When I racked to secondary, though, I noticed it started darkening gradually from the top-down, and now the whole carboy is much darker, somewhat alarming since it looked so pleasing and light in primary.

What might cause this, and should I be worried? It's a half batch, so about 2.5 gallons in volume.

Thanks

Beer clears from the top down, and as the yeast drops out it appears to be darker (since the yeast is white).

If you take out a sample, you can see that it's much lighter in the glass.

I don't see any reason to secondary a wit, but I assume that is in the Brewer's Best instructions? In any case, once the gravity is stable for at least three days, it can be bottled.