In September 1942 Spruance ordered the use of 5N for the Pacific Fleet. http://www.researcheratlarge.com/Ships/S19-7/1942SeptemberPacificCamouflage.html
At that time, the U.S.S. Chicago was in Sydney under repair for bow damage prior to returning to the U.S.
So was Chicago ever in 5N when operating with RAN ships? If not, then it is likely that the RAN colour called Chicago Blue was actually based on 5S not 5N.
The Australian War Memorial has several shots of Chicago during her time in the South West Pacific and under repair in Sydney