I can understand Lexi and Duck colors, after all she's the girl and normally girls have the pink color... more because is a femenine color... well.. she could choose blue or another color... but I understand why they give to her that color.
Duck is easy... he's black and orange without the suit... so is normal he has orange (can you see duck with a green beak??? or red one... no... he look cool with the orange
So... why a bunny will have the color yellow??? or Rev has red??? Tech green??? And Slam purple???
It was because they wanted???... or the color look good in them??? or have a significant???
Normally leaders are red, black or blue... but this time is yellow... why??? (I love that for one time the leader doesn't have the "normal leader color")...
I'd think it would be because of what the colors generally "represent." For example, red is the color of passion and energy. Green is cool and relaxed. Yellow can be bright and fierce; it also stands out. Orange is somewhat of a less liked color. Pink is generally associated with girliness and such things. Purple... well, I'm not sure about that one. xD When I first started watching LU I couldn't even decide whether Slam's color was purple or blue.
Go to the analysis area on the forum and there is a topic called "Cali, do you mind if I put my analyses here?" There you will find for each character, I put an analysis for, including Slam. So, if you get stuck let's say, it will give you an idea.
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... I'm not an anti-Rev. I just really love Kuzco.
Except for Slam, the analysis part of this site has some good explanations. My favorites are Tech and Rev. Red can mean anger, love, danger, activity, and a bunch of other things I can't remember. Green can mean generosity, health, and misfortune (the last one REALLY makes sense). Anyhoo, I highly reccomend reading there.