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ML Flower Meanings in VADD Chapter 90
In leaked screenshots of Chapter 90, where they announce the placements of the hunting competition's participants, the four MLs— Derrick, Reynold, Winter, and Callisto— are shown surrounded by flowers.
Of course, all of us know that SUOL-nim is fond of putting small details into her work(and I make my English teachers proud by overanalyzing things), so here's a quick breakdown of the flowers and their meanings.
Derrick Eckhart: Blue Hydrangea

Hydrangeas are a multitude of species, the majority of which are native to East Asia. Their name comes from two Greek words, which together mean "water vessel". This refers to the shape of the flowers, but can also be to this genus's tendency to need a lot of water. Hydrangea colors can be all over the place due to soil pH, and in theme with that, they have varied meanings, especially when taking into account different cultures.
Blue Hydrangeas symbolize regret, apologies, and forgiveness.
This could mean that Derrick is regretting how he treated Penelope and is trying to ask for her forgiveness(unlikely, but let a girl dream). Perhaps it can also be Penelope's regret in trusting Derrick during the trial, and him immediately blowing that chance to high heaven and into hell the second he opened his mouth.
Sidenote: I originally thought they were chrysanthemums because I got blinded by ML sparkles. (I need to sleep.) I'll add my original explanation for chrysanthemums below.
Blue Chrysanthemums, which I thought Derrick was depicted with, symbolize a love that is over and how the person has gotten over the pain.
It could be referring to how Penelope no longer trusts Derrick as of the end of Season 2, and how she has decided his route to be unviable.
Blue is also the color that Derrick is associated with throughout the novel: his ribbon, his clothes, and not to mention, the teaser image dropped during the series' release countdown.
Reynold Eckhart: Pink Roses

Roses are a ubiquitous sight in any situation that necessitates. With over 300 species and tens of thousands of human-bred variations, roses can have many different appearances and meanings. Even a difference in the shade can have a new meaning.
Reynold is shown with pale pink roses in the background. The specific variety is unknown, but it looks like a Belinda's Dream Rose or a Royal Highness Rose to me. Both of them have the pale pink color and classic rose shape(which I have no idea whether or not there's a rose species for that common shape) and also the petals curl down and form semi-triangular shapes.

Belinda's Dream on the left, Royal Highness on the right
Light pink roses convey a sense of femininity, grace, and comfort. They convey gratitude and sympathy.
Perhaps, like with Derrick, the pink rose symbolizes Penelope and Reynold's emotions towards each other. Gratitude towards him for believing her during the trial, and Reynold's comfort and sympathy towards his sister.
Pink is also the color Reynold is associated with: not just in his hair color, but also in promotional images as well.
For novel readers, we know that Reynold's affection indicator turned pink and that the colors share meaning with rose colors(at least speculated to be so).
Callisto Regulus: Red Roses

Again, as with Reynold's section, roses are ubiquitous and have many different meanings. I'm not sure about the rose variety, but they look to be the same 3D asset.
However, I would like to take a shot in the dark and say the red roses in his panel are Chrysler Imperial Roses or Super Hero Roses.
Chrysler Imperial Roses I chose for the way their blooms are tight with the outer petals being looser and curling in to form triangular petals. They are said to have thick stems with noticeable thorns.
Super Hero Roses are not as tight, but share the triangular petal curls and have bright oval-shaped leaves. They also look very overexposed when photographed because of their brightness.

Super Hero roses on the left, Chrysler Imperial Roses on the right
Unlike Reynold's pink roses, Callisto's red blooms are seen with rose thorns, something that was overlaid with Eckles' introduction in the beginning chapters of the manhwa, denoting his danger.
Red roses symbolize love, passion, commitment, faithfulness, and loyalty. They denote reciprocated romantic love and a strong relationship.
Unlike Reynold, I think Callisto's roses are mostly his feelings towards Penelope, and no, I'm not saying this as a Callisto main.
Throughout the story and in the future of the manhwa, Callisto is steadfast in his loyalty to Penelope, committed and faithful to his love for her. Of course, those who have read the novel also know that Callisto is the endgame ML, and his gauge color becomes red.
(I'm sorry I somehow wrote so much for Callisto even though he was supposed to have the least— Reynold already had the explanation about roses)
Winter Verdandi: Wisteria

Wisteria is a vining shrub and member of the pea family. They can come in various shades of purple, white, or red. They can have many different meanings, but symbolize romance in the cultures where they are native.
It's seen as a symbol of everlasting wisdom because they can grow for over a century, and their sprawling vines represent the continual search for knowledge.
Mauve wisteria means "passion, hidden beauty, intellect and wit, and devotion".
Lavender wisteria conveys "delicateness, refinement, grace, wealth, and royalty."
White wisteria, which can be seen in the panel, implies "healing, purity, health, youth, rebirth, and mourning."
In Korea, wisteria symbolizes a devotion that transcends death.
In VADD, Winter has a secret identity as an information broker and a wizard. The continual search for knowledge and eternal wisdom is something that is characteristic of Winter. He's also one of the most refined and gentlemanly of the MLs.
Fans of the novel will know that Winter rewound time and is the cause for the time loops, all to let the original Penelope have another chance at defeating Leila.
The white wisteria may primarily mean "rebirth", tying back into the time loop that he created.