"The green and the red apples are falling too."
Translation:A zöld és a piros alma is esik.
If it is a general statement, Hungarian tends to use the singular.
But the plural version should also be accepted. But then the verb will also be in the plural:
"A piros és a zöld almák is esnek."
(That is, the red apples and the green apples.)
On the other hand, if you are asking why the verb is in the singular when we have at least two apples in the sentence, that is a difference between English and Hungarian. When the subject is a list of single items, the verb is usually in the singular in Hungarian. We could even say it like this, clearly with two subjects:
"A zöld alma és a piros alma is esik."
The subjects are all single items, the verb stays singular.