I don't think purple is a neutral, but it does go with far more colors than I thought. Obviously, black, grey and cream or white are basics, but certain shades of blue work very well, too (given that purple is a combination of red and blue, that makes sense). And fuscia or the right shade of pink work well, too.
In the winter, however, my coat is normally black or cream, so regardless of what I am wearing under the coat my purple bag always coordinates with my outerwear!