If you have always had regular cycles with normal menstrual blood flow, this mid-cycle bleed is definitely abnormal. Ovulation is sometimes associated with some amount of spotting along with pain. The altered color is perhaps due to some old blood. Also, the possible rupture of a cyst
should be borne in mind. Either way, a sonogram of the pelvis, preferably in the trans-vaginal route along with a speculum examination should be able to help you out. Hope this helps.