hi
i finally figured this out with a little help from Gregor.
to change the colour, right click on your desktop and select properties.
Click on the appearance tab. Click on advanced, select 'selected items' from
the Item drop down box and then change the 'color 1' box to the desired
selection colour.
once completed click ok and then click apply.
this will then change the colour you select in excel to the colour you
requested. it will also change the colour other items are selected in, i.e.
outlook emails etc, but it works