More likely than not it was vaginal fluid, which can thicken and change in color both depending on the level of arousal AND the time of the month (vaginal mucus is already thicker and stringier at ovulation; if you are using the family planning method they tell you to check for that as a sign of ovulation).

If it eases your worries, as others have said, don't let him finish inside you for the duration of your sexual relationship. You can take the morning-after pill if it's been less than 72 hours, but remember that its effectiveness level drops the farther you get from the time of intercourse. I would also recommend getting back on the pill if you plan on being sexually active at all. It's relatively inexpensive and will keep you more protected if you choose to have sex without having so much worry.