Yeah. I can believe that Trini was an accident. They wanted two girl rangers. Blue, Red, and Black are "boy colors" whereas Yellow is neutral.
And Zack's character was pretty normal for the era (black guy who incorporates "hip hop" into everything he does) but there is zero chance it was not intentional to cast the Black guy as Zack the Black ranger.
And yeah. Even as kids on the playground we all knew that was racist as shit. I'll always remember my homeroom teacher trying not to laugh her ass off while she was telling us we can't talk about how they should have cast a Native American as the Red Ranger.