All the doctors, nurses and surgical equipment assigned to each girl were also colour-coded. The girls are expected to remain in hospital for at least a week, Crameri said.
Australian surgeons have successfully separated conjoined twins after a tense and lengthy six-hour operation.
Bhutanese paediatric surgeon Dr Karma Sherub first campaigned to bring the twins to Australia with months of negotiation and fundraising by the Children First Foundation.
They headed into the theatre at 8am on Friday, and doctors planned to administer the anaesthestic about 8.45am.
Elizabeth Lodge, from the charity, said Ms Zangmo was feeling "a little bit scared" about the procedure, but had shown "extraordinary calmness" so far.
"The success of surgery depends on where the twins are joined and how many and which organs are shared, as well as the experience and skill of the surgical team".
She spent Friday praying and meditating. "She tends to ... always be on the top, pulling rank, as we say, and Dawa's more placid", the spokesperson said.
Dr. Joe Crameri, head of pediatric surgery at Melbourne Royal Children's Hospital, said Friday that the surgery was a "relief" and a "joy".More news: French authorities ground Ryanair plane over cash row
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"She still has this extraordinary calmness about her, which is just wonderful".
The surgery to split Nima and Dawa was originally scheduled for last month, but was delayed to guarantee they were in good shape for the grueling operation.
Mr Crameri said there was no significant bowel attachments that complicated the procedure and the main challenge was to reconstruct the infants' abdomens.
One of the biggest operating theatres has been commandeered for the procedure, which will involve two teams of anaesthetists - one for each sister.
Dr Sherub first met the girls when they were only a day old and played a major role in getting the twins to Australia, having already spent time in the country as the victor of a medical scholarship.
"Especially Dawa, as she has not been moving much. She's struggling because Dawa is holding her back".
In 2009, the same hospital performed a successful operation to separate Bangladeshi conjoined twins.
Because doctors in their home country are not equipped to separate them, the twins flew to Australia last month for the important surgery.