The way light is diffused within a room can make even exact colors appear a little different. If the pieces are on opposite walls, you might never even know the difference. If you are worried about matching, then choose a contrasting, but complimentary color and it will look intentional. Good luck!

Take a door from the vanity down to Sherwin-Williams and have the color matched. Then paint the linen cabinet.

Silly question: When stores and manufacturers list vanity linen towers as 18" wide, are they talking about the exterior width or interior width? In other words, is the interior width of an 18" wide tower really less than 18"?

Widest part of the exterior.

Leslie,
Keep in mind that if the cabinet has any trim or crown wider than the body, then it is the trim width that is usually measured.