In one of the many remarkable flukes of this series, the printer managed to match exactly the colors of the early printings for this 1951 issue. Almost all other stamps in this series that were printed in 1951 and thereafter have colors that can easily be distinguished from previous printings.
Here are two specimens with their corresponding watermark scans. Notice that the plates are dirty and/or worn out.
Here is a 5p1L1 with dark colors.