Sub Macro1()
'default yellow 65535
Set rngTemp = Range("A1:A10")
For Each cell In rngTemp
If cell.Interior.Color = 65535 Then cell.Value = "4"
Next
End Sub
The number 4 looks like a ColorIndex rather than a Color; try this...
If cell.Interior.ColorIndex = 4 Then cell.Value = "100"
While assigning "100" will work (Excel seems to do a behind the scenes
conversion and makes it a number), there is no need to put the quotes around
the 100, this will work as well...
If cell.Interior.ColorIndex = 4 Then cell.Value = 100