Since the release of IZ*ONE's La Vie en Rose, "La Vie en Rose" was produced by the same producer who made CLC's last comeback title track "Black Dress." The song was similar to "Black Dress" as well.
In Hong Kong earlier this year, Elkie spoiled that they would comeback in July or August. The members continued to spoil their comeback to fans. On May 13th, (until this day, CLC has yet to comeback.)
In CLC's reality show (which was just released on November 1st) CLC was told that they would have a comeback soon.
This was recorded on May 11th or earlier (this is according to Eunbin's instagram post since she was wearing the same top as she was in the clip.) In episode 2 of the reality show, the members talked about the concept of their comeback.
They talked about having a strong (girl crush) concept with the song having a strong bass beat yet being soft. This description fit "La Vie en Rose" perfectly.
After this speculation, a video was leaked (now deleted) on twitter with the choreography of IZ*ONE's La Vie en Rose with CLC's version of the song playing.