Thanks for your repluys Chaps.
David, I can't use the conditional Format tool (I don't think) as I
have in effect 2 contitional formats to apply to each cell, but as far
as I can gather one always has priority over the other so both can not
be applied at the same time.

I got my selectionchange event to work but found it quite slow in
updating the cells every time you selected a cell let alone changing it
so I have set it to run with a button as essentially it only needs
updating when more data is imported into the file.

Thanks again for your time.
Donna