Maybe color shouldn't map to textfont.color

plotly.js seems to impose smart defaults for text color anyway, for example:

Note that if you change split to color, you can't see the text!!

zoo_dat <- tibble::tibble(
  animal = rep(c('giraffes', 'orangutans', 'monkeys'), 2),
  count = c(20, 14, 23, 12, 18, 29),
  zoo = rep(c('SF Zoo', 'LA Zoo'), each = 3)
)
plot_ly(zoo_dat) %>%
  add_bars(
    x = ~animal,
    y = ~count,
    text = ~count,
    textposition = "auto",
    split = ~zoo,
    stroke = I("black")
  )

Start by reproducing the supplied plot_ly/add_bars example in R and inspect how plotly.js assigns textfont.color when bars use split = ~zoo. Compare the output after changing split to color; done means the text remains visible under the reported smart-default behavior.