Usualy whites have the lead because they move first.
So whites play the opening they like, and get into diferent variations depending on how black plays.
Black will be playing the theory, this is know that opening and play it. Can also play some general defence, like the Indian.
If they get into a move they don't know the theory, then they will play following the principles of the opening, this implicates thinking the moves, wich is time consuming.
Sometimes they will try to force the position to the opening they know, so on the comments they maybe say something like "I play this move becouse it makes the position looks sorta like the Ruy Lopez and I know that position very well".
I am a new player just learning openings. So far I have only used one book opening, the Ruy Lopez as white, and won.
I often hear players talk about their "favorite opening" etc. My question is:
Which player decides the opening? Both players cannot use their favorite opening for each color in the same game, correct? So don't both players need to have an opening reportoire that spans a myriad of openings?