In both the original and remastered versions of this shot, the rear of the warp nacelle appears to be cropped at the bottom.
I don't see what could be legitimately obscuring the nacelle. At the very least, there should be blue glow, and then the underside of the nacelle. I guess it was an error that HTV never caught.
In the remaster, with the exception of the deflector and engines, the Enterprise's hull almost appears gray-scale with no apparent greens as someone else already pointed out. Compare how washed out the yellow on the saucer is. Because of the lighting, the rough edges of the saucer also seem to show through, making it look more like the model it is. It looks like it's in need of some touch-up paint.
Even at a smaller resolution, the smaller ship closest to the frame appears more realistic. I hope in motion, the models don't appear so flat.