Function GetCellColour(r As Range) As Long
    GetCellColour = r.Cells(1, 1).Interior.Color
End Function

Function GetCellColourIndex(r As Range) As Long
    GetCellColourIndex = r.Cells(1, 1).Interior.ColorIndex
End Function

=IF(GetCellColour(A1)=65535,"Cell is yellow","")

=IF(GetCellColourindex(A2)=6,"Cell is yellow","")