A creamier, warmer undertone is also more appealing in MN, especially during the winter, when straight up white can be harsh in the cold weather.
You could also try to get a paint fan deck from your local paint store take it to the property and try to find the match. (Hirschfields, SW, Lathrop, etc. will usually give you one if you show you are a remodeler or similar)
Hope that helps!
All kidding aside, paint color tends to change slightly over time. If you have a smart phone you may download an application from any of the major paint companies that will allow you color match the walls. My favorite is Color Smart from Behr.