This is somewhere between description and Analysis. It does not reach into either one of the other two which require either interpretation or judgement.
I don't think it is simple description. The writer is saying that the color forms a contrast, between first of all the pale blue of the background and the striking color of the mother's clothing. The washed out colors of the background leads us to the clothing. It's a contrast, well pointed out, but so far there is no meaning attached to it.
The second contrast does the same thing. The children are very young and their color is pink (sort of) which suggests youth and health. Again, no particular meaning is put on that. It is merely an observation.
