When do you use black acrylic paint out of the tube?

The most appropriate time to use the black paint out of the tube is to determine if the painting is going to be warm or cool and then go from there. I prefer to mix my black paint but if I do use it out straight of a tube I find that is best for abstracts or silhouette. If you don't use black paint correctly it can throw the entire painting off especially if you are going for a natural realistic painting.

Will the cold freezing temperature damage my acrylic paint if I leave them in the car?

Yes freezing cold temperatures will damage your acrylic paints. The pigments and water generally separate from the acrylic vehicle. They can thicken and have a tar like appearance or form chunks among other things. Most of the time the paint cannot be put back into a state of emulsion for stable adhesion to a canvas surface.

Can you use purple to make shadows?

Many artists choose to use dioxazine purple or a purple blend of their own for their shadow mix. If you are going to use purple for your shadow be sure that it will blend in with the color palette you are using.