This is actually not all that uncommon. Flushing during sexual stimulation is usually more common in females than males, but it can occur in both genders. The following is taken from Wikipedia:
"Commonly referred to as the sex flush, vasocongestion (increased blood flow) of the skin can occur during all four phases of the human sexual response cycle. mStudies show that the sex flush occurs in approximately 50-75% of females and 25% of males, yet not consistently. The sex flush tends to occur more often under warmer conditions and may not appear at all under cooler temperatures.
During the female sex flush, pinkish spots develop under the breasts, then spread to the breasts, torso, face, hands, soles of the feet, and possibly over the entire body. Vasocongestion is also responsible for the darkening of the clitoris and the walls of the vagina during sexual arousal. During the male sex flush, the coloration of the skin develops less consistently than in the female, but typically starts with the epigastrium (upper abdomen), spreads across the chest, then continues to the neck, face, forehead, back, and sometimes, shoulders and forearms.
The sex flush typically disappears soon after orgasm occurs, but this may take up to two hours or so, and sometimes intense sweating will occur simultaneously."
So, unless you have chest pain or other symptoms associated with the flushing, it is probably nothing to worry about. Though most people do get the change in coloration along with the flushing, some only get the increased heartrate and congestion of the veins in the head and neck.
If you are really concerned about it, or have other symptoms, you may want to discuss it with your physician. Good luck.