"Mark" wrote...
Its weird - I can see exactly how it should work and if I use the custom
format

[Black]0%;[Black]-0%;[Black]0%

in different worksheet it works fine. But even if I copy and paste-special
this format to my existing worksheet it still refuses to change from red
when the % is negative.

I'm completely stumped. Any ideas?

What's the number format of the cell that's displaying the negative
percentage in red? What the cell's font color? Has one of your friendly
colleagues changed the 'black' color to red in Tools Options Color?