Conditional Formatting Upon Paste

I am trying to make each Cell in a range of cells to change its color from Black to one of a few colors. This should happen when the value of the Cell matches one of a few possibilities. The problem begins when I want the value of Sheet1 Cell A1 to come from Sheet2 Cell B1. When I change the value in Sheet2 Cell B1 the format of Sheet1 A1 changes only when I click on that Cell. How can I make it change immediately when I paste my values in Sheet2? Here is the code I am using on Sheet1:

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim icolor As Integer
If Not Intersect(Target, Range("A1:A10")) Is Nothing Then
Select Case Target
Case "one"
icolor = 1
Case "two"
icolor = 2
Case "three"
icolor = 3
Case "four"
icolor = 4
Case "five".......................