Modifying your code a bit:

=====================
Option Explicit
Sub GreenPhrase()
Dim s As String
Dim c As Range
Dim i As Long, j As Long

s = InputBox("Which phrase to green?")
j = Len(s)

For Each c In Selection
With c
i = InStr(1, .Text, s)
.Font.ColorIndex = xlAutomatic
If i 0 Then
.Characters(i, j).Font.Color = RGB(30, 255, 15)
'Selection.Interior.ColorIndex =
[A1].Interior.ColorIndex
End If
End With

Next c
End Sub
+++++++++++++++++++++++++++++

Is this modification making the code running faster?