leaves turning purple?

Okay, here are some observations. Autoflowers are genetically related to plants from shitty areas (environmental pressures), so they try flower as quickly as possible. In shitty areas, often, you have cold and low light, short growing season, so the plants try to reproduce as fast as possible. Due to that, they deplete themselves quicker (such as using phosphorus from numerous parts of the plants to flower). Another thing is, anthocyanins (red to blue pigmentation, most often purple or even black) is related to what is essentially a combination of those factors (like strain adaptation to environment, nutrient availability, stress, low light, etc). So a plant that wants more heat and light or phosphorus (or is using a lot of it), will often turn purple or black. Phosphorus deficiency (relatively speaking) is most commonly related to that anthocyanin production, along with calcium and nitrogen, as those factors are very related (from what I've seen).

Don't worry about it. Your plant is fine. It is nothing to worry about and completely normal in some strains. Trying to fix something that is not a real problem will take longer than the plant has left in its life. It will not affect your plants growth rate or potency in the slightest. Some plants turn almost black by harvest time, especially if night temps are low. Honestly, it is nothing to be concerned over and is not a problem. Hope this helps,........... Organoman.

Is this Maria Antoinetta? If so, what is your amendment schedule? Given the age of the plant, and that it's an auto, it very well may be the plant using it's energy stores; aka, it's getting toward the end of flowering. Otherwise, it could be nutrient buildup, but I didn't see any mentioned in your grow. Leaf tip burns this late im flower means a lack of nitrogen. If you plan on harvesting in two weeks, maybe hit them with a little nitrogen via some compost tea. If you're close to harvest, probably best to let her cannabalize the nutrients from those leaves I would think. I'll defer to smarter minds, but my two cents say it's nitrogen deficiency due to you're getting close to the end of the plants lifecycle. Cheers, and hopefully you figure it out!