If the nuclei are reddish-brown in color rather than blue-purple, they have not been sufficiently blued—increase the time in the bluing reagent.
Reddish-brown nuclei may also indicate that the hematoxylin is past its expiration date and needs to be replenished with a new batch.
This top image is a slide that did not go through the bluing step.
The bottom image is a slide that has been properly blued.
