In full light, you can only achieve true white color with a ref value of one. Lower values gives darker results. JDA is perfectly right about the pure white settings.
Boosting the Emit value will “false” your render, as if you totally turn off all your lights, the object with a Emit value will still be visible (proportionally to the Emit value, of course) so I feel this should not be the way to make real white colors, as your render would not behave reallistically (but it could be your purpose, anyway).
Finally, you can also turn on the Shadeless button in the material context buttons if you want to achieve a pure plain color, as defined by the RGB and Ref values, along with the lamp Energy inetnsity, without shading or self-shading of the faces.
Hope this helps,