'Benötigt wird: 1 Picturebox
Private Sub Form_Activate()
 
Dim i&, j&, Farbe1&, Farbe2&
 
Farbe1 = vbRed 'alte Farbe
Farbe2 = vbYellow 'neue Farbe
With Picture1
Set .Picture = LoadPicture("C:\EinBild.bmp")
.AutoSize = True
.AutoRedraw = True
.ScaleMode = 3
For i = 0 To .ScaleWidth - 1
  For j = 0 To .ScaleHeight - 1
    If .Point(i, j) = Farbe1 Then
      Picture1.PSet (i, j), Farbe2
    End If
  Next j
  DoEvents
Next i
End With
 
End Sub