Ce véhicule, la voiture de mon oncle, (il) est bleu.
"la voiture de mon oncle" is an apposition and does not affect the adjective ending in the clause. For example.
Appositions don't count for purposes of agreement. There is only one subject and an apposition which does not affect the masculine, feminine ending.
Only the subject does. What counts are two or more nouns. Like this: Les camions et les voitures de mon oncle sont bleues (la règle de la proximité). Some people prefer : sont bleus (le masculin l'emporte sur le féminin).
Those terms explain how people decide what to make the adjectives agree with. You can either have the adjective be feminine if there are two nouns, and the feminine noun is closest to the adjective (in the case above, those noun voiture is feminine) OR you can use the masculine if you think the masculine ending carries the day over the feminine, as a general principle. There are explanations that say that the masculine is actually a Latin neuter but I am not getting into that here.
It gets complicated by political correctness and recent social movements.