You have to extract as much detail as possible out of the B/W picture and then combine it with the RGB picture (I assume that you have a mono camera here).
The RGB picture is only there to provide the colours and not much extra detail.
The picture doesn't look bad at all and has plenty of detail.
It looks as if the colour data has been taken a bit out of focus and gives bigger stars.
I doubt you have lost much detail overall. The first colour image looks like it may have been squeezed a bit hard which can make the overall noise level increase quite some.
The real answer to detail lies in the quality of the focus and the signal to noise ratio which is largely dependant on the total exposure time. 27 X 120 isn't a whole lot of exposure to work with.
The second image looks better but still needs the extra exposure to give it a kick.
Still it's a very nice image.