Picture a house with no foyer. The entry door opens right into the living room. At a right angle to the entry door, trim to trim, is a closet door. Both of these doors are the same 1950's light brown veneer grain doors, sort of like this:
So you're looking into the corner of the living room and you see 2 "matching" doors at right angles. When the entry door is open, it hides the closet door completely.
Now, consider replacing the entry door with a fiberglass that the owner wants painted to match the shutters and trim on the front of the house, sort of a maroon color.
What do you do with the inside of the entry door? Do you paint it the same maroon (which won't really match the color scheme of the room) or do you paint it to match the room which won't match the other door or do you paint the door to match the room and replace the closet door with something similar and then paint both doors to match or ... ?