UPDATE:
So this happened a week ago, last Friday. I called the dealer and they gave me an appointment for the following day, Saturday. I took the car to the dealer and explain to them about the leaking and showed them some pictures I had taken. They also agreed that it must be the coolant. "Luckily," the car started leaking when I was at the dealer and they could see what I was dealing with. After giving it a good inspection, they found that the radiator had a tiny hole which was causing the leak. How that hole got there, they couldn't tell. Anyway, I told them (and they knew) that I had just had the car serviced there in January and that my 3-year warranty had just expired in that same month. I left the car there over the weekend and they told me they would contact Mazda first thing Monday morning and try to have them cover the repair with the warranty. Monday came and they told me that Mazda would not cover the repair ... but the dealer would! Long story short, I got my car back on Wednesday. They replaced the radiator and I didn't have to pay a penny (not even to replace the gas in the loaner car I got)!