Cell Colour Pallett Changing...........
 

Using Excel 2003 SP3 I have a strange problem whereby the available colour
pallett for cell shading seems to change of its own accord.
For instance, I have set a number of cells to shade orange via conditional
formatting. I left the file open this morning while going to make a cuppa
and, on my return, the orange cells had changed to a wierd brown colour and,
on opening the cell colour pallett, sure enough, the orange option has
disappeared to be replaced with brown.
This is not the first time this has happened and its not connected to
conditional formatting as I have experienced it before on spreadsheets with
no conditional formatting.
Does anyone have any idea what happening and why please? More imporantly, is
there a way I can prevent this happening?
Many thanks
Kind regards
Peter