My first son changed by around 10 weeks, but they can change up to a year old I've heard. And actually his eyes have lightened in the last year or so (he's now 2 1/2). Still waiting to see about ds#2 (he's 3 mths, 7 weeks adjusted) . . .
Ds had very dark blue eyes at birth so we knew straight away they would be a browny colour, they were definite brown by 4 months. DD had the same dark blue and had chocolate brown eyes by 4 months. #3 however had light blue eyes at bitrh and at 9 weeks (now) they are chrystal blue like those husky dogs have (like daddy). I was really excited and must admit that you guys have burst my bubble now that I know they can still change .