This is a Hindu tradition and it is not permissible for Muslims to practice it. However, if all Muslims practice it now without any imitation to the Hindus and there is no mixing  and no non mahram would see this, this is permissible.

I wanted to know if it is allowed to participate in the pre wedding henna/mehndi parties common in the indian subcontinent. I have heard the hadith where our prophet says he who imitates a people is of them. I am of the understanding that this celebration is from the hindu culture. If the event was within our sharia guidelines (no free mixing or music) would it still be impermissable due to the background of the ceremony? Is there any basis in islam for celebrating it?