The redness is due to the dilation of the blood vessels, which increases the amount of blood that passes through them. In this way, they acquire a deep red color.
Just like on the face or neck, the vagina suffers a similar redness. This tag must be used when there is a blush in that area or near it
Depending on the character's species, the Blush can change from being red to the equivalent of said species. Use this tag in that situation as well.