I apologize if you've already said so and I missed it, but I'm assuming the saucer is not designed to separate from the rest, and perhaps the nacelle itself is intended to be ejectable?
No, the saucer is not separable, but the space warp nacelle definitely can be ejected if it poses a threat to the rest of the ship. Also the nacelle can be swapped out for a replacement either in the case of irreparable damage or for an upgraded unit.
I've been thinking about colour and I'm inclined to go with something closer to my initial idea of a darker hull overall. I'm thinking of variations in tone of the basic colour and not too much in the way a contrasting colours. I'm thinking the overall colour to be a medium to light grey with a bluish tinge to it. I guess I'll have to experiment.