We always laugh at a video of my now 20yr old nephew talking about his 2 grandads at age about 3/4 yrs. He talks about 1 grandad and says he's very Black (he's Sudanese) then says but my other grandad (my Dad whos an aged ex ginger) is very Bright. I have studied child development and remember doing a piece of work about stages of development, not sure if it was moral or personaltity development, but I had to get children of various ages to describe a person the youngest wrote the persons name and he has black hair and wears glasses, the next youngest, also described mainly physical qualities but added he is nice, this progressed through the ages to more personal qualities being described rather than physical. So focussing on different physical attributes is developmentally appropriate at this age. My youngest daughter unfortunately commented on her older sisters "very fat" friend, it's hard to explain that it's not nice to say that, without creating a situation where she thinks fat is wrong, if you know what I mean.