I agree that the "butterfly" part applies to Fielding's daughter (I think there's even a line in the episode about her "breaking out of her cocoon" or something). I've got a few ideas as to what the rest of the title might mean.

1.) It could be a reference to the nature of Fielding's radio show (and his personality and relationships with other people) - that he sees the world in only black and white but that there are in fact "shades of grey" that have to be considered.

2.) It could be a reference to the bland world in which Victoria is trapped. Look at the pictures in the site's Episode Guide - the photos of Fielding and his offices are oppressively grey and bland. There's hardly any color there at all.

3.) The title also sounds a lot like the title of a painting, which would make sense if the episode dealt with art in any way. But it doesn't.

Maybe? I don't know. The title is just as baffling to me, but those are some of the ideas I came up with.

I always thought the "Shades Of Grey" was an overt reference to the Monkees song of the same title. That's kinda to do with non-specific loss over a period of time - and, yes, Fiedling's daughter was the butterfly.
Fielding knows he'll lose her, as all parents eventually do, but he can't help but try and hold on to her.
Well, it makes sense to me anyway