Riot, Star Guardian Poppy should have some blue effects.
https://pbs.twimg.com/media/Csvtx7xUkAA3cjJ.jpg
In her splash art we see her star buckler is blue. Yet in game when thrown it is yellow.
https://m.youtube.com/watch?v=4A4P3O0uQuI
Sure there is a tiny blue comet trail, but I feel that it isn't matching with the splash art.
As for her other abilities, people argue that because she's melee you can't change the looks of her abilities that much without confusion. Would changing her W to have more of a blueish tinge really effect the clarity that it's being activated? Or making her E blue so it more accurately fits with her being the blue shooting star? I can understand not changing the colors of the Q because that has a delay (though does Taric's stun color change with his skins? I know Ekko's W does).
Was Poppy's the last skin to be made? Would that explain the lack of blue in her abilities?