I'm going to guess that there's a window to the left of the desk?
The blue highlight on the edge of the desk looks like daylight
coming into a tungsten balanced scene. Your best bet is to first
control the lighting (or at least be aware of what the different
light sources do to color), then control the exposure. You're still
going to have to post process most of the time if you want really
good color, but this is true with film as well...and all digies.
Again, shooting raw or at least using custom white balance will get
you a little closer out of the camera.
I was following the advice from Scott Kelby's book. He suggested
that if, after shooting, you sample each point from the grey card
your photo will be dead on.
...and mixed light sources (as previously stated) is the major
reason why. It's no different using Tungsten/Daylight film. Also,
by correcting in Photoshop, you may get a true white, but you'll
probably through other colors in the image off (either hue, value,
or saturation).
Shoot the gray or the white of the 'gray card' and use custom white
balance to set that as the white value. That will get you close,
but with any light capturing device, you're gonna get mixed results
when your light sources are different temperatures. That's why a
photostudio has 100% controlled lighting.
--
My images:
http://michael972.smugmug.com
--
http://www.dougridgway.com/dpreview/urb_01/
