Concrete Stain

my driveway has a very large area that is covered with a stain that looks like someone's radiator boiled over. it appeared after snow and ice melted. the driveway was about 3 or 4 months old. the builder came and cleaned it but it came back. there are many other spots on the driveway that are not near as big but the same color. the builder said that they are from the yard being fertilized.  could you please give me your opinion as to what these spots are from and if there is a remedy for them? thank you
I am afraid there is not enough information in the email.

How did they clean it? Did they manage to completely remove it? What does "came back" mean?

The "fertilized" excuse does not make sense.

Is that a dark or light stain?

Dark stains are usually an indication of moisture coming through the concrete.

By itself it is no threat to the concrete.  It may mean that the affected area is more porous than the rest, but that may still be structurally fine.

If you are very concerned you may want to call a local concrete-testing laboratory and have them sample the concrete.  This may be expensive and not too helpful.

Sounds like the builder was very responsive.  Maybe you can work with them to test it.  Most likely it is not a major problem, but you will have to do some more investigation.