What formula you using

As the site mentions defauly is cell colour.

Determines cell colour (interior) or text colour (font)
' Default is cell colour
Need to use a formula like (Note the true for font instead of cell)

=SUMPRODUCT(--(ColorIndex(A1:A100,TRUE)=3))

Also you have to press F9 to recalc which also may look like it's not working

VBA Noob