S.C.
Hi J.,
Not sure what the rust color looks like, but I can tell you from my own experience with my EBF daughter that at 4 weeks she slowed to pooping only once a week and her poos became smooth like pudding or toothpaste and the color has been a medium color brown. Still smelled the same. Ped hasn't been concerned. My other daughter (fraternal twins) poos more regularly but she also transitioned to smooth poo soon after her sister.
S.