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.
Nuclei that are reddish-brown may also be an indication that the hematoxylin is beyond its' expiration date and needs to be replenished with a new, fresh 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.
