Here is a general reference on mineral deficiencies, with
pictures of tomato leaves for examples:
http://4e.plantphys.net/article.php?ch=5&id=289
The symptoms of phosphorus deficiency shown in that
document are quite a bit more severe than simple purpling
from cold temperatures. The pictures in the first post in this
thread in another forum are closer to the mark:
http://www.helpfulgardener.com/phpBB...ic.php?t=15657
(High pH can interfere with phosphorus uptake, too, which
may have been that person's most significant problem. See
this document for a general overview on the relationship
between pH levels in soil or container media and phosphorus
uptake:
http://www.selectedplants.com/OrthoPhosphate.htm
)