My Own IT dept wrote:
I created at template in which the plot area color is bright yellow and
applied to a chart. When I re-opened the file the color turned to magenta.
I've had other problems with cell colors changing on their own also.

Any ideas?

Thanks.

I'm on a thin limb here, but what version of Excel are you using and
have you checked the color palette? I have noticed more than once using
Excel 2003 that the color palette changes "sporadically" sometimes and
this might affect the rendering of pre-existing files.