hello! thank you for the question :DD

Anzu is usually associated with pink, and it's most likely her favorite color too! most of the stuff she owns that we see across different enstars media are pink items (pink cardigan, pink phone case, pink pens, pink raincoat, pink umbrella, pink notebooks, pink lunchbox etc.). well pink is the girl color and most joseimuke mcs are associated with pink so that's understandable :DD

as a bonus, while not a favorite color, anzu is also associated with red :DD that's because most of her cameo outfits consists of her wearing a red outfit (the red dress in the subaru card meant to represent her, her miko attire, her red riding hood costume) and in a valentines day line by keito he says that anzu looks really good with red ദ്ദി ( ᵔ ᗜ ᵔ )

Another bonus color associated with Anzu is white! that's because as the mc, she's a "white canvas" for the players who want to project onto her in the real world, and is one in canon as well being a new producer who knows nothing but is full of potential at the start of the game's story (although I've heard people associate that image with more with Tomoya since that fits his character's story). an old post I love to reminisce about was one someone made about how the four colors of the trickstar members hokuto-blue subaru-orange makoto-green and mao-magenta are found diagonally from each other, with white in the center that can be interpreted as anzu too :)) (wow trick5tar so perfect)

for Tenn-kun, I actually don't know much about /him/ specifically to be able to answer that, nor am I fully deep into the engirls fandom to be able to tell what the fans associated with him (ㅠ﹏ㅠ) I tried reverse-searching anything involving color with him, to no avail but maybe my research was just insufficient, I'm sorry!

for my personal opinion though, in my mind i associate him with white much more than i do with anzu, due to most of his cameos being him in his white polo and black pants so he's always seen in plain white, which helps further emphasize how much of a blank slate he is in my eyes (and well he is honestly a way more of a self-insert protagonist than his sister)

I guess it's notable that that in one his cameos in the EnGirls 4komas, he was wearing blue pajamas, so that's something I guess (ᵕ—ᴗ—) ngl i would like to associate tenkousei-kun with blue the most more than white since most households appropriately assign pink and blue to siblings (especially when they are twins or two opposite sex)

if I missed anything in engirls about tenkousei-kun's favorite color, i'd love to know that too if someone else out there knows :DD i'm skeptical that they'd even mention anything for him specifically but you never know right (˶ᵔ ᵕ ᵔ˶)