A gold standard for Eta and its colour balance is probably here
(Daniel's work is extraordinary)
http://www.verschatse.cl/nebulae/ngc3372rgb/maximum.jpg
What also needs to be understood is the amount of exposure given to an image will affect its relative colour balance. The core of the Carina Nebula
is very bright and it will saturate to white if the surrounding (quite red) nebulosity is being captured with some depth.
To preserve this dynamic range and still make an image look "natural" is not easy. But probably most would agree this has been done well in the linked image.