Both rules remain in effect as they do not contradict each other.
If a joker tile occupies a space on the wall of a certain color, you MAY NOT place tiles of that color in the corresponding pattern line any more.
Any vertical or horizontal line on the wall may include several joker tiles.
Basically joker tiles are joker tiles and are not placed as other tiles.
For placement blocking purposes they will assume the color that is on the wall beneath them.
Since the variant board has no colored spaces, the joker tiles will never block the placement of other tiles (joker or otherwise) on the variant board.