gt data_color extension to target column

my_data_color.R

my_data_color <- function (data, SOURCE_columns, TARGET_columns, colors, alpha = NULL, apply_to = c("fill", 
                                                            "text"), autocolor_text = TRUE) 
{
  stop_if_not_gt(data = data)
  apply_to <- match.arg(apply_to)
  colors <- rlang::enquo(colors)
  data_tbl <- dt_data_get(data = data)
  colors <- rlang::eval_tidy(colors, data_tbl)
  resolved_source_columns <- resolve_cols_c(expr = {
    {
      SOURCE_columns
    }
  }, data = data)
  resolved_target_columns <- resolve_cols_c(expr = {
    {
      TARGET_columns
    }
  }, data = data)
  rows <- seq_len(nrow(data_tbl))
  data_color_styles_tbl <- dplyr::tibble(locname = character(0), 
                                         grpname = character(0), colname = character(0), locnum = numeric(0), 
                                         rownum = integer(0), colnum = integer(0), styles = list())
  for (i in seq_along(resolved_source_columns)) {
    data_vals <- data_tbl[[resolved_source_columns[i]]][rows]
    if (inherits(colors, "character")) {
      if (is.numeric(data_vals)) {
        color_fn <- scales::col_numeric(palette = colors, 
                                        domain = data_vals, alpha = TRUE)
      }
      else if (is.character(data_vals) || is.factor(data_vals)) {
        if (length(colors) > 1) {
          nlvl <- if (is.factor(data_vals)) {
            nlevels(data_vals)
          }
          else {
            nlevels(factor(data_vals))
          }
          if (length(colors) > nlvl) {
            colors <- colors[seq_len(nlvl)]
          }
        }
        color_fn <- scales::col_factor(palette = colors, 
                                       domain = data_vals, alpha = TRUE)
      }
      else {
        cli::cli_abort("Don't know how to map colors to a column of class {class(data_vals)[1]}.")
      }
    }
    else if (inherits(colors, "function")) {
      color_fn <- colors
    }
    else {
      cli::cli_abort("The `colors` arg must be either a character vector of colors or a function.")
    }
    color_fn <- rlang::eval_tidy(color_fn, data_tbl)
    color_vals <- color_fn(data_vals)
    color_vals <- html_color(colors = color_vals, alpha = alpha)
    color_styles <- switch(apply_to, fill = lapply(color_vals, 
                                                   FUN = function(x) cell_fill(color = x)), text = lapply(color_vals, 
                                                                                                          FUN = function(x) cell_text(color = x)))
    data_color_styles_tbl <- dplyr::bind_rows(data_color_styles_tbl, 
                                              generate_data_color_styles_tbl(column = resolved_target_columns[i], rows = rows, 
                                                                             color_styles = color_styles))
    if (apply_to == "fill" && autocolor_text) {
      color_vals <- ideal_fgnd_color(bgnd_color = color_vals)
      color_styles <- lapply(color_vals, FUN = function(x) cell_text(color = x))
      data_color_styles_tbl <- dplyr::bind_rows(data_color_styles_tbl, 
                                                generate_data_color_styles_tbl(column = resolved_target_columns[i], 
                                                                               rows = rows, color_styles = color_styles))
    }
  }
  dt_styles_set(data = data, styles = dplyr::bind_rows(dt_styles_get(data = data), 
                                                       data_color_styles_tbl))
}

library(gt)

  # Add function into gt namespace (so that internal gt functions can be called)
  
  tmpfun <- get("data_color", envir = asNamespace("gt"))
  environment(my_data_color) <- environment(tmpfun)
  attributes(my_data_color) <- attributes(tmpfun) 

  # Test
  
  data <- data.frame(cat = LETTERS[1:3],
                     M_SD = c("1.1 (0.7)", "3.5 (0.6)", "2.0 (0.7)"),
                     M = c(1.1, 3.5, 2.0))
  
  # DESIRED code
  gt(data) %>% 
    cols_hide(3) %>%
    my_data_color(SOURCE_columns = 3, TARGET_columns = 2, 
               colors = scales::col_numeric(palette = c("red", "green"), domain = c(1, 4)))