I am not an expert, but I would leave it alone and just call your vet, and ask the question over the phone. I have seen rusty color milk in horses. I have seen really thick yellow nearly orange.
In humans colostrum comes in many colors and I have even seen a weird shade of green and it was STILL fed to human premies.
However there are a LOT of people on this board that have way more experience than me.
I just wouldn't want to see you milk her out trying to clear it up before a foal is born.
JMHO,
Robin