Good catch~! What really stands out to me in this panel is the fact that is is shaded black even though the panel is colored

Maki in general very interesting. Sheer utility of it is insane (which i will come back to in a bit) and it could also be a very interesting direction Oda can go with Sanji's conqueror's Haki. There some folks in the Japanese fanbase already theorizing that in additon to 覇王色 (Haoshoku/Sovereign), what Imu could potentially be showing us is 魔王色 (Demonic Sovereign) which is a pretty interesting take considering that everytime character's feel Imu's haki it's akways described as malicious. For example, we've experienced both Joyboy and Imu's haki and even though range wise they are the same, charcteristically they feel fundamentally different.
On the utility bit, though it actually makes my Sanji demonic transformation theory very feasible bcoz rather than Oda going the route of PoL giving Sanji the ability to transform or even going down the route of ancient demon race genes giving him the ability to transform like I previously speculated, he can just have Sanji utillize Maki to form wings, or even horns without it being an outright pyhsical transformation

I initially theorized that Sanji will prolly awaken Conqueror's Haki on his next Jambe power up giving the pattern Oda seems to be going with but might as well turn out to be Maoshoku.
悪魔/Akuma/Demon (Diable) ⇨魔神/Majin/High Class Demon (Ifrit) ⇨魔王/Demon King (????)
One trait of Maki that Sanji prolly won't have if Oda does go that route is the animated effect Imu's flames seems to have akin to Big Mom's Homies. Reckon it's a direct result of his awakening rather than it being a charateristic trait of Maki itself.