Appliances and plumbing should always be white (the house I grew up in had pink and green toilets!), and walls and floors should be neutral (white-tan). Anything referred to as a 'new classic' should be avoided. Today's stainless fridges are yesterday's avocado green ranges. Basically, no one should be able to know much about you by looking at the non-removable elements of the house. It is okay to choose soft furnishings and accessories you like, since you can easily recover pillows, and put your Betty Boop collection in storage. Actually, anything very personal should be removed when it's time to sell, so people can imagine your house with their own touches.

Also, they're totally NOT timeless, but I really like wall stickers. They're cheap, easy to apply, and easy to remove. We got some from Ikea for our bedroom because we're not great at decorating. They take up one wall, but could be gone in five minutes.