Is it a weed?

Some say this pretty flower is a weed. It certainly seeds itself at will, but it is so pretty I let it flower where it will. Does anyone know it's name! Some of the flowers come up mauve.

Excitement last evening when I was part of our WI team that came first in the Village Week Quiz! We beat seventeen other teams (the Tennis Club, the Conservatives, the U3A etc) and went home with the cup. The problem is that the winners have to organise next year's Quiz! We will cope, we have done it before.