Erst einmal einfach:

Sub Gelb3()
    Dim ws As Worksheet
    Dim Zeile As Long
    Set ws = ThisWorkbook.Sheets("Tabelle1")
    ws.Activate
    For Zeile = 1 To 100
            If Cells(Zeile, 1).Interior.Color = RGB(255, 255, 0) Then
                Cells(Zeile, 3) = "Test"
            End If
            If Cells(Zeile, 2).Interior.Color = RGB(255, 255, 0) Then
                Cells(Zeile, 3) = "Test 1"
            End If
            If Cells(Zeile, 1).Interior.Color = RGB(255, 255, 0) And _
                Cells(Zeile, 2).Interior.Color = RGB(255, 255, 0) Then
                    Cells(Zeile, 3) = "Test, Test1"
            End If
    Next Zeile
End Sub