When making chardonnay wine, after the primary fermentation and 1st racking, we added sparkloid (as per instructions) and the wine immediately changed color. Why is this?
Its because the sparkloid pulls stuff in suspension out of suspension. Solids in suspension tend to make the wine (or beer) look lighter in color because it reflects more light back at you, as that stuff settles out the more light passes straight through and it appears darker.
Nothing to worry about.
To see this effect in action put a tsp of flour into a glass of red wine and stir. It will look very light in color. Then as the flour settles out it will get dark again.