You didn't mention if they were in pots or a garden. In a garden, either way they could be too dry. Another reason could they have gotten hit by the late frost? Have you watered them since transplanting. Were they in the sun in the nursery or in a greenhouse. Some plants that have been in a greenhouse need to be hardened off before transplanting. They may be getting too much sun for tender plants. All these are reasons for the yellowing, without further information I can't be sure.