Who knows, he could go either way. My yorkie, Sully, has changed from darker to lighter this past year, too...
http://www.yorkietalk.com/forums/showthread.php?t=39478 - there are before and after pics!
But I noticed that though he didn't have an itchy-allergic reaction to the flea meds (frontline plus)......my groomer said that's why he has a big patch of thick, black hair growing in where I put all the summer flea meds on him! Isn't that crazy?!!