We use turn to talk about visible changes of state. It is common before color words. Note that turn is more formal than go.
- Leaves turn brown in autumn.
- When I broke the news she turned red.
- She turned white with anger.
- Suddenly everything turned black and I became unconscious.
- He turned nasty after he had had a couple of drinks.
Note that in British English go is more common than turn.
To talk about a dramatic or sudden change in the nature of somebody or something, we use turn into. Note that turn into is used before nouns.
- Jealousy can turn even the nicest guy into a monster.
- When the princess kissed the frog it turned into a prince.
- Everything that Midas touched turned into gold.
Turn is also used to talk about people changing their religion or occupation.
- Towards the end of her life, she turned Catholic.
Fall means ‘become’ in a number of fixed expressions. Examples are: fall ill, fall asleep and fall in love.
- She fell in love with an old guy.
- The child has fallen asleep.
- he falls ill more often than other kids her age.