My 14 month old son vomited what appears to be red/pink in color. Should I be concerned?

My son woke later than normal this morning. For breakfast he had mini muffins, a banana, and milk. My noon he was ready for a nap so I laid him down. He slept for three hours which is a bit abnormal but not alarming. While he was napping I heard him coughing a bit. (He's recovering from a cold.) When I went in to wake him up I noticed he had vomited in his sleep. What concerned me was that the liquid appeared to be pink or reddish in color. Since he's been up he's had 7 oz of milk and some graham crackers. He has not vomited again but has been coughing on and off. Is this alarming enough that I take him in to Emergency or just monitor to see if it happens again. He has had a bowel movement since getting up and that was normal. The picture is of his mattress cover when I took his sheet off his bed.