I recently transplanted a bunch of corn flowers and they are turning purple and red. I also have lupins, tomatoes, and sun flowers turning red and purple. When I transplanted them i dug the hole twice as deep and filled the difference with soil, 3 in 1 and 1/8 of a teaspoon of organic 4-4-4 fertilizer and lightly watered it before placing in the seedlings. They were all hardened off prior and had not been fertilized in ten days. Last fertilizer i used was a 2-2-2 fish emulsion at half strength. I thought I might have over fertilized but I have some that haven't been transplanted that look the same. What could the problem be and what can I do?
I’m posting this comment, not really an answer, in hopes of closing the question. For plant species and varieties that normally are green, red leaves are a sign of stress. I’ve seen it mostly in overwatered plants and occasionally in dry ones. But red leaves can come from any kind of stress. That’s why the comments all ask for more information. People are trying to help you diagnose what kind of stress your plant is suffering.
Here are two plagiarized comments, with sources: “Fluctuations in the soil and air around plants upset nutrients and cause red pigments. Cool spring air and cold soil often produces red and purple foliage tints. ... High soil salts draw water away from plant roots and create droughtlike conditions that cause red leaves as surely as true drought. https://www.hunker.com/13406045/why-are-my-plant-leaves-turning-red-during-summer
“Red geranium leaves signal the plant is stressed in some way. This may be because the plant is receiving too much water or too much sunshine, or has been planted outdoors too early or in mineral-deficient soil. Geraniums that are planted too close together also tend to develop red leaves.” https://www.gardenguides.com/about_6538075_geranium-leaves-turning-red_.html