green
The color change, though physical by itself, is caused by a chemical change of some colored substances in cabbage.
When adding tomato juice to cabbage juice, the cabbage juice turns redish
For the chemical composition of cabbage see the link below.
reversable
Yes, adding lemon juice to limestone causes a chemical change as the acid in the lemon juice reacts with the calcium carbonate in limestone to form calcium citrate, water, and carbon dioxide.
For the composition of cabbage see the link below.
Because tooth paste is a base because anything that turns a blue or green when mixed with red cabbage juice(indicator) is a base.
When red cabbage juice is mixed with baking soda, a chemical reaction occurs. The baking soda is a base and reacts with the anthocyanins in the red cabbage juice, causing a color change. The mixture will turn blue or blue-green due to the change in pH.
Reversible
Chemical, physical is generealy changes between the states of matter, although those are not the only physical changes
Alkali turns red cabbage juice blue or purple due to a chemical reaction with anthocyanins in the cabbage. This color change can be used as a natural pH indicator.