I'm surprised that I have not written about this topic in the past, as it occurs daily. We have 3 self-powered scooters at our house. Unfortunately for me, they are all different in color. My 7 year old was riding the blue one and my 3 year old wanted it. I told him that there were 2 other scooters available for him to ride. But of course, "I want the blue one." No amount of reasoning or convincing could deter my 3 year old from getting his hands on the blue scooter. I made all kinds of promises to my 7 year old to give his younger brother the blue scooter. You can play on the Nintendo DS, you get a juice box, you can be a good big brother etc... Well finally, with a lot of reluctance my 7 year old agreed and dropped the scooter about 3 feet away from his little brother, at least to have a little victory that his little brother had to walk to the scooter. Less than 5 minutes later the little brother was no longer interested in scootering, blue, yellow, or any color for that matter.
My wife and I try to buy 2 or 4 of the same exact things whenever we pick up new things. The scooters unfortunately came at different times, so we could not coordinate the colors. It doesn't really matter, because whatever your brother has is always better than what you have, so I must have it.