To be fair. It all depends on what the starting colour is that you're trying to make white.
Making black into white for example, is rather difficult due to the enormous differences in levels.
Turning a colour into white, though.. isn't as difficult..
Take this red bike i've just found for example. Select what you're wanting to change (Usually, you should use a Pen tool.. but I used the colour range, just to save time)
Larger URL at
http://upload.wikimedia.org/wikipedi...s/c/c2/BMX.JPG
The first thing that you want to do.. is to desaturate it. I created an adjustment layer, and desaturated it all completley. Depending on the environment, 100% desaturation might not always be a good idea.. due to reflections onto the white
Then add a new adjustment layer, levels. The trick is.. to make things white, whilst trying to keep the careful balance between the highlights and shadows. I used the following...
Which then gave me the following
In your image > adjustments - there is a whole range of tools that's designed to help with level/colour correction. This was a simple one.. but other things you may want to consider include
Curves
Contrast
Channels
EDIT: Oh yeah, you can see why the colour range tool is BAD.. the whole bike frame now has a white glow to it
