Sick greenfinch or mutation?


For the last couple of days I have been waghing the greenfinches coming to my garden. One definitely looked sick and after he came, I washed everything. 

The first one i saw sick was actually quite lethargic and looked big. The other one are not lethargic at all but looked different. I have attached few pics, sorry if they are not great, I was quite far.

What do you think?

Thank you.