Colony site selection/World map: Growing period viewmode

[zgrssd]

When selecting a site to settle, one figure is among the most important ones:
How long the Growing period is.
A hex with 20/60 is leagues harder to survive in then one with 40/60.
While a 60/60 would be trivially easy on the food front.
The need for hydroponics and refigeration is directly dependant on that figure.

At the same time when doing caravans, I would like to see which tiles is forageable right now. This is not so much a indicator of growing season lenght, but if growing is in-season right now.