...
I... Wasn't expecting THAT. That's for sure.
On a serious not though, I saw a clear panel of a black flower when she transformed there, which is pretty interesting for a couple of reasons. First, we never really found out what the black flower is/means thanks to Imitatio's interruption when it happened to Baiser, but Venalita seemed to know how it working and it appeared to be more important than just a random visual effect.
Second, when Baiser bloomed, that WASN'T actually her La Verita. The form she took when she went out of control was a different one, so It's possible this isn't actually Magenta's La Verita, and is instead a different transformation like the one Baiser went through when she got white hair and dark skin.
Third, if this is similar to what happened to Baiser, this might be a completely insane and unhindered Magenta rather than just a lewd looking one, which could be a real issue. When Baiser lost control things got REALLY bad, so hopefully this won't be a repeat of that.
Forth, Baiser believed her loss of control was directly caused by Venalita's influence, and if so, it's extremely likely this is happening to Magenta because she was infected with Baiser's powers at that time, which could have some interesting repercussions.