The answer is COMPLICATED!
Almost everything affects anthocyanin production: light, temperature, stress, pH, minerals, and moisture. So, not surprisingly the colors are all over the place and also why semps vary in color so during the season.
Right now I'm trying to select for those that keep at least some color year round. Killer for example never looks the same but always has some color phase. It is a red/ green bicolor right now. When I started growing semps, NONE of the semps retained their color in the summer. This has all come about through our breeding. Jungle Shadows was the first that did it for me and it passes this trait along to its progeny. Right now I have some huge purples that retain their color year round.
A study by a European showed that the soil in cavities where semps grow is ~pH 4.5, something that would grow good blueberries or cranberries! I never add lime to the soil although some are in beds bordering bearded irises which are limed. The all-semp beds are never limed. My soil is ~6-6.5. You can tell this yard was once solidly in Douglas firs.
Kevin
