Unfortunately, the information is not consistent. For example, California Polytechnic State University says the tree grows in USDA Plant Hardiness Zones 9 to 11. The Missouri Botanical Garden says the tree grows best in zones 10 to 11. The difference in the minimum temperature in zone 9a and 9b might be important with respect to the plant’s successful growth. Zone 9b has milder winter temperatures than zone 9a.
If you want to grow a rainbow eucalyptus where you live, it would be best to consult a local expert who has experience with growing the tree in your climate or who has knowledge about the likelihood of growing the tree successfully in your area. A local person can probably offer you the best advice. Some places have small areas with a microclimate that is warmer than the hardiness zone data for the area indicates, which is something else to consider.