This is the 14042nd most frequent German word.
gelber
"Gelber" means "yellow" in English (comparative or masculine form).
In this sentence, 'gelbe' is the attributive adjective form of 'gelb', agreeing in gender (neuter), case (nominative), and number (singular) with the noun 'Auto'.
Das gelbe Auto gehört meinem Bruder.
The yellow car belongs to my brother.
Here, 'gelben' is the attributive adjective form in the masculine accusative singular case, agreeing with 'Saft', the direct object.
Ich mag gelben Saft zum Frühstück.
I like yellow juice for breakfast.
In this example, 'gelbe' is used attributively in the plural form nominative case, matching the noun 'Blätter'.