Learning how to visually identify a colour cast - how?

The simple way to educate your eye in LR is to literally play with the Temp and Tint sliders. You'll easily be able to tell when there is too much blue/yellow or green/magenta and, over time, you'll get a sense of where the sweet spot is. You can also use the Auto setting as a starting point to give yourself an idea what LR thinks. The alternative is to do formal color cast removal (black point/white point/gray point) correction in Photoshop.

Hope this is helpful.

Jeff