You can modify conditional formatting "on the fly" using code.  For example:

Public Function SetColumnBackground(ctl as Control, NewColour as Long)
Dim fc as FormatCondition
With ctl.FormatConditions
   If .Count = 0 Then
       Set fc = .Add(acExpression,,"1=1")
   Else
       Set fc = .Item(0)
   End If
End With
fc.BackColor = NewColour
End Function

To set a column background to bright green:
   Call SetColumnBackground(Me("Control1"), RGB(0,255,0))

Note that this assumes conditional formatting is not being used for anything
else.  If it is then your code would need to do a bit more work.