I agree with NdAppy. The common usage of "tricolor" is actually a bay or brown tobiano. This filly looks brown tobiano to me. A legitimate tricolored horse is very rare and is usually caused by chimerism (two sets of DNA in one animal).
I'd clip some fur around the babies eyes to see if there's any grey under there. If not, I'm going to vote brown tobi. Haven't seen a pic of mom, buckskin/grey doesn't make sense to me, she's either buckskin or she's grey???