Does 那个公共汽车很红 sounds right?
It is not 'all adjectives in Chinese are verbs' but 'many adjectives in Chinese can also function as verbs' and most of the time you need a correct verb particle
Examples:
黑马 - Black horse (O)
天黑了 - The sky has darkened (O)
把墙黑了 -  to darken the wall (X) - the correct verb is 涂黑(to paint black) or 弄黑 (to make black)
瘦狗 - thin dog (O)
這狗瘦了 - This dog has thinned down (O)
瘦自己 - to thin oneself down (X) - the correct verb is 弄瘦 (to make thin)
強人 - strong person (O)
這人強了 - this man has grown strong (O)
強這攻势 - strengthen this attack (X) - the correct verb is 加強 (to strengthen)
攻势弱 - the attack is weak  (O)
攻势弱下來了 - the attack has weakened down (O)
弱他们的攻势 - to weaken their attack (X) - the correct verb is 減弱 (to weaken)

那个公共汽车很红 sounds right?


红(red) here is still an adjective for the noun 公共汽车 (this bus is very red)

红 (short for 火红 = popular and trendy) could function as a verb with an appropriate verb particle


Example:
那种公共汽车最近红了起來 = Recently, that kind of bus has become popular and trendy