VBA Matching >1 Value In A Loop?

If the following macro matchs two ID numbers from column B in column C it shoud highlight them green.

Column C may has multiple entries of column B, however the macro i have written appears to only match the first ID number found in column C from B.

I think this may have something to do with my loop, can anyone suggest a solution?

Sub colour_filter()

Dim myrange As Range
Dim Rng As Range
Dim rng1 As Range
Dim a As Integer

Set Rng = ActiveSheet.Range("B2", Range("B" & Rows.Count).End(xlUp))
Set rng1 = ActiveSheet.Range("C2", Range("C" & Rows.Count).End(xlUp))
a = 0

For Each myrange In Rng
If IsNumeric(Application.Match(myrange.Value, rng1, 0)) Then
rng1(Application.Match(myrange.Value, rng1, 0), 1).Range _
("A1", Cells(1, Columns.Count).End(xlToLeft)).Interior.color = vbGreen
a = a + 1
End If
Next myrange

MsgBox "Number of matches: " & a


End Sub