Sub ColorVowels()
Dim c As Range, d As Long
For Each c In ActiveSheet.UsedRange
c.Font.Color = vbBlack
For d = 1 To Len(c)
Select Case LCase(Mid(c, d, 1))
Case "a", "e", "i", "o", "u"
c.Characters(d, 1).Font.Color = vbRed
Case "y"
c.Characters(d, 1).Font.Color = vbGreen
End Select
Next
Next
End Sub