Nikon D300 Complete Manual page 321

4. Use the Direction pad to highlight the white balance
option you want and press the > key to select it.
5. If you've selected a Fluorescent setting, use the
Direction pad to highlight the type of bulb that
dominates the lighting and press the > key to select it.
6. A new wrinkle (with the D3 and D300) is that you are
next given the chance to fine tune the white balance
using a two-dimensional plot.
The B (blue) and A (amber) axis is essentially
equivalent to color temperature. By moving the
position of the black dot along this axis you can cool
(towards B) or warm (towards A) the overall color
Thom Hogan's Complete Guide to the Nikon D300
V1.02
Page 321