Some time ago, someone asked why one of the MCDUs (the computor display unit in the aircraft) was displaying in white.
The normal Flight plan has green alphanumrics (characters, letters and numbers for all you university types), with the occasional blue - see below. All on a black back ground.
Currently, some MCDUs use white for the Alternative Flight Plan which is always white, i.e. all the letters and numerals are in white on a black back ground. the alternative flight plan is used instead of the original flight plan or as a back up to the original. (I.e., it is the Original, copied, but with different bits in it, like an approach to a different runway, for example, or a piece of flight plan to take you to an alternative.diversion airport, complete with an approach, which the pilot(s) have typed in.
There is also a Temporary flight Plan, the alphanumerics here are displyed in Yellow and Orange, a temporary flight plan, is a flight plan that is undergoing changes being made to it by the pilot such as diversion to an alternate or other change to the flight plan (same aircraft same system) There are also blue characters - these are usually pilot enter(able) information, i.e the pilot can put in his/her own information or leave it alone, ie., cruise flight level.
Some of the alphanumric characters are in red, these are either red boxes that must/can be filled in by the pilots or some warning messages, are also in red - like UNABLE CRUISE FLIGHT LEVEL which is telling the pilot that his her choice of FL is either too high or otherwise unsuitable according to the computer, given all the information available to it.
If, as was the case, one MCDU is displaying normal green characters, and the other is all white, then one pilot has the normal, current flight plan displaying and the other pilot is cross checking or making adjustments to the alternate flight plan.