dc589da6_iew_of_Canon_s_pro_digital_SLR__Description
[Setting] Custom WB [Colour Temp. (Kelvin)] 2000K-10,000K [Description] 
Colour casts are neutralized based on a previously-taken image of a neutral object (the EOS-1D user guide recommends a white piece of paper). The object must fill the spot metering circle.
Rob Galbraith DPI: Canon EOS-1D: a preview of Canon's pro digital SLR
Description