You need to use VBA to do this. Try something like this:-

Select the range from start to finish and then run this code - assumes your
cells are either coloured or not, and that if they are then they get
numbered.


Sub NumberColour()
Dim ActSht As Worksheet
Dim cel As Range
Set ActSht = ActiveSheet

ActSht.Columns("C:C").NumberFormat = "0000"
cntr = 1

For Each cel In Selection
If Not cel.Interior.ColorIndex = xlNone Then
cel.Value = cntr
cntr = cntr + 1
End If
Next cel
End Sub


Regards
Ken....................

"Dave" wrote in message
...
Hi

I would like to auto number cells that have only a light yellow colour.
In Row C sheet1 I have numbers starting from 0001 etc, some cells in the
column do not have light yellow these remain blank.
So if a Row C cell becomes light yellow i would like the next number to be
added.

Thanks in Advance