I've noticed that this is a BIG question on-line so I thought I'd post my opinion to add to the masses. Why is yellow so hard to choose? Because all colours get twice as bright when they get bigger [all over the walls] and it is well known in colour theory that yellow is the first colour the eye sees, it's simply the brightest. Which is why it has to be toned down (or muddied) even more than the other colours, before it becomes a 'designer' yellow on the walls.
Flickr
The reason why I'm calling it 'designer yellow' is because a professional colour consultant spends a lot of time 'toning down' colours that their clients choose in addition to helping the client pick colours that create flow in their home. A pretty paint chip does not necessarily make a pretty wall colour and it's also why one client said to me "I am ALWAYS surprised when I see the little 2" x 2" chip all over the walls, it's never what I thought I would be".When I first did my colour training in San Francisco with the Daystudio, I came home and bought all the colourant so that I too could shift the colour on site [like I had been trained to do]. In the end though, the only colour I was able to change reliably [on-site] was YELLOW. For example, the way you actually get to 'beige' is by adding the 'complement' to the colour you are working with. So if you want pinky beige you start adding 'green to red' if you want a nice yellowy-beige, add 'purple to yellow'. My students spend 2 classes, right at the start, painting with colourant, toning down the colours, etc so that they can start to understand how colours are created.
Therefore, if you want to tone down a bright screaming 'laundry room' yellow, add some purple to it. Or better yet, take your gallon back to the paint store and ask that they 'tone it down' for you. So don't worry, if you've picked the wrong yellow, you can always muddy it and add some orange if it's too green. It's going backwards that you cannot do without adding a lot of white paint to an existing colour--which I don't recommend, cause who knows what you'll end up with, at that point, it's better to start with a fresh gallon of paint.
Ford actually called this colour 'Screaming Yellow"
Image from flickr
You certainly don't need a 'light' with this kind of yellow. When the yellow above gets toned down, it would then work on an exterior wall like the one below:
Image from flickr
There are painters and colour consultants that arrive on site with their colourant kit and 'shift the colour' on-the-spot if it's not right. After actually working in a paint store though, I really got what a science adjusting colour is, so I would rather let the experts perform their magic in the store with the shakers to get it perfect!