If the order is a week old then it will not even have been given a build slot so just call and change the colour.
Regarding keeping popular cars in stock you need to google the way car manufacturers make cars today, they use the Japanese system called “Just In Time” where they only hold parts in stock for the cars they have orders for up to 6 hours prior to the actual build, ring round a few dealers and ask what cars they have in stock like the Allspace.