Blood in the semen can cause a pink or reddish colour, known as hematospermiaand may indicate a medical problem which should be evaluated by a doctor if the symptom persists.
The Psychology of Semen, Part Two: Your Questions Answered
Some of you wondered whether hormonal birth control or the "depth" or the relationship could have affected the results of the study. The findings may seem like a stretch, but before you cry foul, consider that a number of studies have shown the same correlation from unprotected vaginal sex. Continuum International Publishing Group, p. Plus, he adds, "It may very well be the case that the anti-depressant properties of semen are dose dependent, and that repeated insemination may be necessary to get the effects. Ditto if he wears briefs.