It could be accepted. But 'Bananas are yellow' is kind of a general truth or fact.
In Hindi, when you refer to such 'general truths' or what you call the 'habitual form', we use the verb 'होना' and conjugate it like any other verb.
So a more precise translation would be 'केले पीले होते हैं' . Another example, Mangoes are fruits. - आम फल होते हैं।
The notes in the Animals skill explain this point.