Hi,
Anytime you notice a change in your discharge that seems abnormal or odd to you, you should consider making an appointment for a pelvic exam w/ a gynecologist. Yellow or
green discharge is usually indicative of a
vaginal infection (and sometimes possibly STD's). Since you do use condoms and don't believe he's a risk, it's possibly a minor infection (yeast or BV) that can usually be easily treated by your doctor.