My colours in the palette disappear at time when using Excel 2003
 

Recently when using/downloading Excel worksheets or templates I have noticed
that colours disappear from the palette (usually the bright green). If
I hover the cursor over the missing colour then the words "colour scheme"
are displayed rather than the name of the colour as is usual.
This has happened on numerous occasions & on differnet worksheets. I have
repaired sokme,deleted ones that may be corrupt, etc but this continues to
hapen & is frustrating as I need certain colours to complete reports. Can
anyone suggest what may be occurring. This has only happened since using
upgrading to Windows XP & using Excel 2000 & 2003