Use VBA to change colors of slide elements in Powerpoint 2013
This should get you a step closer, though I'd probably rewrite it as a function that you could pass lFindColor and lReplaceColor to.
Sub ReplaceColors()
Dim lFindColor As Long
Dim lReplaceColor As Long
Dim oSl As Slide
Dim oSh As Shape
Dim x As Long
lFindColor = RGB(255, 128, 128)
lReplaceColor = RGB(128, 128, 255)
For Each oSl In ActivePresentation.Slides
For Each oSh In oSl.Shapes
With oSh
' Fill
If .Fill.ForeColor.RGB = lFindColor Then
.Fill.ForeColor.RGB = lReplaceColor
End If
' Line
If .Line.Visible Then
If .Line.ForeColor.RGB = lFindColor Then
.Line.ForeColor.RGB = lReplaceColor
End If
End If
' Text
If .HasTextFrame Then
If .TextFrame.HasText Then
For x = 1 To .TextFrame.TextRange.Runs.Count
If .TextFrame.TextRange.Runs(x).Font.Color.RGB = lFindColor Then
.TextFrame.TextRange.Runs(x).Font.Color.RGB = lReplaceColor
End If
Next
End If
End If
End With
Next
Next
End Sub