A much better solution, but not free (but cheap), is using a Pantone Huey.
I've nattered on about this many times in the past, but it is a very cheap and accurate solution really.
http://www.ausmedia.com.au/dynamic/c...Pantone%20Huey
For $99 (or $189 for the Pro version if you've got multiple monitors), it does a great job.