Public Function fnSumByBackground(rngRangeToSum As Range, rngPattern As Range) As Double
Dim varColor As Variant
Dim rngIterator As Range
varColor = rngPattern.Interior.Color
For Each rngIterator In rngRangeToSum
    If rngIterator.Interior.Color = varColor Then
        If IsNumeric(rngIterator.Value) Then
            fnSumByBackground = fnSumByBackground + CDbl(rngIterator.Value)
        End If
    End If
Next
End Function