I found this peach-leaved bellflower (Campanula persicifolia) at the side of the road. It's a British wild flower but the species is also grown in gardens, so this may have been an escape.
Looking the plant up, I found its blue colouration and the blue and violet colour found in all 550+ known Campanula species is due to a compound called Violdelphin, one of a group of compounds, called flavonoids, which plants manufacture, and which benefit plants in a variety of ways.
In the UK six or more other bellflowers grow wild, including harebells and clustered bellflowers.