It sounds like they are too cold at night as purple on the foliage and pale leaves are a sign that the plants are struggling with cool temperatures. Tomatoes like night temps above 50 degrees. You can cover the plants with Remay which is a spun polyester blanket to keep in heat, or make a mini greenhouse with hoops of pvc over the plants and a covering of bubble wrap. I am not sure what zone you garden is in, but most areas of the US still have cool nights until June. Next year pot up your plants and move them indoors at night until mid June. Keep growing, Marianne Binetti