Why don't you try the suggestions you've had? You've had step-by-step
instructions as to how to apply either conditional formatting or custom
formatting. [If you can't find the Conditional Formatting button to which
pub referred, use Home/ Styles/ Conditional Formatting. Similarly Custom
Formatting can be found under Home/ Cells/ Format/ Format Cells]
If you are saying that you want Excel to change its behaviour without you
giving it any commands, then sadly it won't do that, because Excel doesn't
know what you are thinking, and it needs you to tell it what to do.
If you want the conditional formatting or custom formatting to apply to a
range which covers only part of your sheet, then select that range before
you apply the CF or custom formatting. If you want to apply it to the whole
sheet, select the whole sheet either by Control-A or by clicking in the
top-left square (above row 1 and to the left of column A). In either case,
the conditional formatting or custom formatting will apply the colouring to
the cells that meet the specified conditions, and not to those that don't.
(pub's example in custom formatting would have made a zero green, but you
can adjust the format to suit your own requirements, so perhaps
[Green]General;[Red]General;General )
What else did you want?