Blue flowers (and I mean really blue flowers!) are few and far between and lots of nursery people call anything blue that could be lavender, mauve or purple as they know it will sell things. Look at all those things being called “Blue Roses” for instance.
In late summer and autumn a small deciduous shrub from China with intense blue flowers is this under appreciated plant that not only flowers for months right up until the real cold weather tells it to give up but when it is time to stop all its leaves turn red (usually with lots of flowers still about, which is stunning!). When it is all over in winter cut the plant to the ground like a herbaceous perennial and all will repeat next year.
It grows to about half a metre tall and always looks its best if planted in drifts so get several. All it needs is a sunny well drained site with a little irrigation in really hot weather. I have plants in 6″ pots at $16.50. finally a new species called C. asperrimum with paler blue flowers has came my way so you should try this one as well! 
