I stopped trusting the paint match cards at the jobber, and the reason is dumb simple
For a long time I'd walk into my jobber over on Route 9 and hold a chip card up to a bumper in the parking lot, and half the time the color looked off by the time I sprayed it in my bay. Turns out the lot was in full shade under their awning while my shop sits in direct sun from about 11 to 3, and that little difference was enough to push me a full shade dark on two silver Toyotas in one month. Now I pull the car out into real daylight before I pick anything, even if it means moving three cars to get one out. Got a metallic green Subaru waiting on me Monday, so I'm curious how the rest of you handle matching in overcast weather.