This is a tricky one, and it does involve some tweeking to get it right, so just use this as a guide. I'm using the same truck as I did in the Create Black thread, because it's already half done...lol...and I'm lazy.

Step 1: Select the body of the vehicle. I use the polygon lasso tool for this.
http://img.photobucket.com/albums/v223/dakotahq/Tutorials/Create%20White/Step1.jpg

Step 2: Hit "Ctrl-C" once, then "Ctrl-V" twice. This should give you two layers of the body of the vehicle.
http://img.photobucket.com/albums/v223/dakotahq/Tutorials/Create%20White/Step2.jpg

Step 3: Desaturate both of the layers by hitting "Shift-Ctrl-U", so you have 2 gray bodies.
http://img.photobucket.com/albums/v223/dakotahq/Tutorials/Create%20White/Step3.jpg

Step 4: Turn off layer 2 so it's hidden. We need to make layer 1 yellow. Make sure you're on layer 1, and hit "Ctrl-U". This should bring up the handy Hue/Saturation box. Check the Colorize Box.
http://img.photobucket.com/albums/v223/dakotahq/Tutorials/Create%20White/Step4.jpg

Step 5: Move the saturation bar until you get a realistic color. If you're on default settings, the color should be red. In this case, it took a saturation of 80.
http://img.photobucket.com/albums/v223/dakotahq/Tutorials/Create%20White/Step5.jpg

Step 6: Now, slide the Hue bar until you get a nice bright yellow. In this case, it took a Hue of 60. Hit OK.
http://img.photobucket.com/albums/v223/dakotahq/Tutorials/Create%20White/Step6.jpg

Step 7: Unhide layer 2, and repeat step 4 and 5.
http://img.photobucket.com/albums/v223/dakotahq/Tutorials/Create%20White/Step7.jpg

Step 8: Slide the hue bar until you have a nice deep blue. In this case, it took a hue of 240. Click OK.
http://img.photobucket.com/albums/v223/dakotahq/Tutorials/Create%20White/Step8.jpg

Step 9: Now, making sure you're on the blue layer, go to the layer properties drop down menu.
http://img.photobucket.com/albums/v223/dakotahq/Tutorials/Create%20White/Step9.jpg

Step 10: Select "Screen" option.
http://img.photobucket.com/albums/v223/dakotahq/Tutorials/Create%20White/Step10.jpg

Step 11: And there ya have it, white.
http://img.photobucket.com/albums/v223/dakotahq/Tutorials/Create%20White/Step11.jpg

I noticed that this is almost "chrome" looking, but thats because of all the reflections in the red. White typically doesn't show much reflection, so in this case, a flatter color or a subject with few reflections would work better. Also, as I said, this may need some tweaks to get it perfect. Mess with the hue's a little bit if you must.

That's a good tutorial. Had to choose the hard reflection vehicle for it huh? lol

If you desaturate first, then adjust your contrast and brightness you'll be good. you might have to make a couple layers to get things to "blend" right though. That should work also.