Colours of cells change
 

Hi
I have a very strange problem that a user is experiencing with excel. He
tells me that it started happening one day after the pc froze for a second.
When he opens any file with coloured cells the coloured cells appear red.
If anyone else open the same file while he has it open or not it appears
normal for everyone else.
If he saves it while it is appearing red and someone else opens the file
then the cells still appear normal and not red. I highlighted one of the red
cells and checked the colour properties and it was set to red...
We have worked out that if he opens a particular file then that's when it
starts to occur to any excel file he opens after that unless he closes out of
excel totally and then starts it up again.
Could this be due to a setting that this file does to the excel overall
settings that then effects all other documents opened and where would i go to
remove this. Also if this is the case why doesn't it effect other machines.
All machines are running the same office xp sp3 with windows vista
thanks in advance for any help