As a former grower of herb gardens, may I suggest a few herbs.
Rosemary has lovely purple flowers as well as needle like leaves
Sage also has beautiful purple flowers and very pretty leaves
Borage more purple flowers
Feverfew has nice little daisy-like flowers
Marshmallow has red and white flowers
Oregano and Thyme are lovely, and come with varients
I also think that Foxglove would be a wonderful plant with beautiful trumpet shaped flowers.
I always loved growing Angelica, but the flowers are mostly white.
I know you cannot do all of these, but just putting this out there for suggestions.