Do I understand this correctly?

foo <- function(color, ...) {
  standardized_color_name(...)  
  color
}

foo(color = 1)
#> [1] 1

foo(colour = 1)
#> [1] 1

Not sure how much I like messing around with re-assigning values. A simpler implementation could be:

foo <- function(color = colour, colour) {
  check_color_colour(color, colour)
  color
}

check_color_colour <- function(color, colour) {
  if (missing(colour)) {
    return(invisible())
  }
  
  if (!identical(color, colour)) {
    stop("both `color` and `colour` cannot be set")
  }
}

# setting only color
foo(1)
#> [1] 1

# setting only colour (turns into color)
foo(colour = 1)
#> [1] 1

# both are identical, that's fine
foo(color = 1, colour = 1)
#> [1] 1

# difference, we have a problem
try(foo(color = 1, colour = 2)) 
#> Error in check_color_colour(color, colour) : 
#>   both `color` and `colour` cannot be set

^{Created on 2022-12-28 with reprex v2.0.2}
We'd have to include @params color, colour but it would keep it explicitly clear to the user.

1. Yes, that is all it does.
2. I don't like duplicating all arguments. It creates visual confusion, especially with the border stuff and all the different colors. We'll end up with 10 different color arguments and a bunch of comparison functions. Therefore I mimicked the ggplot2::aes() approach. The difference to their approach is that they only have a single argument to care about, while we have various. But true, I haven't considered the foo(color = 1, colour = 2) approach. Might want to throw a warning if this exists in parent.frame()

Update: 12 different colors ... we have two for the inner grid and checking with exists() is not enough, because they all exist at this stage. Maybe this will change once you get to #226 *winkwink*.
Therefore I consider keeping it the way it is. After all no harm is done this way. If the user ends up with a unexpected color ... there are more important things to worry about. If their input creates no color at all, fine too. I'd love for R to have a dynamic way to handle this case. Otherwise I simply strive for a consistent user interface.