I think the main secret of color softness is in combination of the ice that is formed from turbid water and early morning sun light. The particles of snow in the shadow areas gives mild blue tonality. Thickness of an ice gives color variations.
Don't you find the B/W shots somewhat flat?
To me the b/w shots win.
You could try "optimizing" them with curves or USM in some way or another of course.
I believe color doesn't add much here, so I'd go for the simpler b/w version which I find very beautiful.