In this image of the Carina Nebula, the object is represented in a different light as opposed to the earlier true colour image. Instead of the usual RGB method of obtaining true colours of deep sky objects, the image featured here is an emission-line filtered image which represents the nebula's chemical composition. In this case, the nebula is photographed using a modified version of what is known as the Hubble palette, in which three filters to isolate Sulfur, Hydrogen and Oxygen emissions are used. The data from these three filters are then mapped to Red, Green and Blue respectively to create a false colour composite as depicted above. Due to the overwhelming presence of hydrogen in the Universe, most of the objects photographed using this palette will therefore appear predominantly green, a contrast from the usual strongly red colours that ionized hydrogen emits when photographed in natural colour. 

This object was photographed from a city centre with severe light pollution, although the use of narrowband filters helped to drastically the extent of its effects.  

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I have also shot this object in true colour, which you may view on this link here.