Can't understand why a colloidal cleaner would be first choice for this kind of problem. They do have some anti bacterial properties but are primarily a degreasing agent.
Milk in cars is one of the commonest problems car valeters come across. Car carpets are either polyprop or nylon and toatlly resistant to water. The milk will have soaked through the carpet into the foam backing behind and may even be pooling in the dimples in the steel bodywork.
Best solution is to saturate and I mean saturate so there is actually fluid on the top of the carpet, with an enzyme product and leave preferably overnight. Extract out then soak with suitable anti microbial such as clensan, microsan microkill etc. Leave this to dwell for about 15 minutes then vac out, don't rinse out.