Are your Tomato Plant Leaves and/or Stems turning purple or red? That is usually due to lack of nutrients. Lack of nutrients can occure if they are placed to cold (makes it unable to extract phosphorus), sometimes if the soil is to wet (overwatered) or if the soil simply has been running out of nutrients. Anyway – I would recommend to repot, place in room temperature, and they will recover.
I had some Tomato Plants that I neglected a bit this season, which gave me the perfect opportunity to share with you guys. This is what some of my Tomato Plants looked like – a bit sad and all leaves were turning purple:
And this is how the same Tomato Plant looks a few weeks after repotting:
In this plant, you can actually see how the leaves are recovering (the leaf in the bottom right corner is still a bit purple).