Question: How come The Chameleon never speaks here or in any other episode he's in with his actual voice?
The Alien Costume: Part 3 - S1-E10
Question: Why did this design of Venom have light blue and pink on the outside? Something to do with the animated style?
Answer: I believe it was just a way to try and show the suit is "oily" or reflective. It also helps define the character's features since otherwise, he'd just be a flat black color. It's similar to how the black suit Spidey had blue outlines. (I don't know why they chose a pink/red color... maybe because red is associated with power/fire/war, so it's a more "evil" color?)
Answer: The producer, John Semper Jr., claimed that he couldn't imagine Chameleon risking revealing his identity by using his real voice. Chameleon can speak in his true form but simply chooses not to.