Answer: I've often seen these symptoms on newly transplanted seedlings. If you got your seedlings from a greenhouse, they've been used to nearly ideal conditions in terms of care - frequent watering, feeding, soil, etc. When you put them out in the garden, they suffer some degree of shock to the roots, which temporarily reduces their ability to take up moisture and nutrients. This combined with full sunshine cause reddening of foliage, which should ease up as they plants get used to their new home. You can help ease the transition by spreading mulch before transplanting, so soil temperature and moisture levels are moderated. Hold off on fertilizer for now, but keep soil moist (not wet), and they should bounce back. Providing temporary shade and windbreaks will reduce the stresses their feeling so they can concentrate on returning to health.
It may also be that these plants were never "hardened off", meaning that they were moved from their cushy greenhouse home to the "real world" of the garden without being gradually acclimated to sun, wind and fluctuating conditions. Hardening off takes only a few days, and makes a great deal of difference in the success of the plants. Hope this helps!
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