I was working with a group of people of various backgrounds over a four day project. From the beginning I had no idea how many people were on the course because I had no register of attendance. On the first day, when I first met them, there were only 10 and the group grew over the first two days. Some people joining, some people leaving.
There wre a group of black girls - women actually - and I never saw them all together until the last day so I never really worked out how many there were. I called V by J's name one day and she was angry. She said many people (teachers) do that and that they - V and J - don't look the same at all. She implied that we just thought all black people look the same. They are both short and dark skinned black and that really was the end of their similarity. I even understood J as African born and V as British so everything about them was different and I could see it - but I knew I had annoyed V and I knew why.
On the one hand she was wrong to think I couldn't see the difference between them - but on the other, I did lump all the black girls together in one group in my mind as a way of picturing the group I was working with as a whole. I did that to everyone, grouping them according to my own catgories, 'race' or colour included, to try to remember everyone...