Conditonal Formatting Macro Ignore Blanks

I have the following Conditional Formatting vba code shown below which allows me to format diffrent ranges according to the values in the cell, What I want to be able to do is that if Mycell.value ="" then do not apply the colorindex value, in other words leave any cell in the range which has a null value unchanged.

Private Sub CommandButton1_Click()
' Conditonal format for New hourly report
Dim Mycell As Range
'SL80range formatting
For Each Mycell In Range("sl80range")
Select Case Mycell
Case Is >= 0.8
Mycell.Interior.ColorIndex = 4
Case 0.7 To 0.79999
Mycell.Interior.ColorIndex = 44
Case 0.00001 To 0.6999
Mycell.Interior.ColorIndex = 3
Case Else
End Select
Next