`colors` argument to `add_trace` is only respected if the trace type *isn't* specified in the `plot_ly` call

I'd expect these two lines of code to produce the same output, but only the first does what I expect (uses the colors argument to pick a palette for the points):

plot_ly(data = iris) %>%
  add_trace(x = ~Sepal.Length, y = ~Sepal.Width, color = ~Species, colors = "Blues", mode = "markers")

plot_ly(data = iris, type="scatter") %>%
  add_trace(x = ~Sepal.Length, y = ~Sepal.Width, color = ~Species, colors = "Blues", mode = "markers")

This seems backwards since I added the type="scatter" to avoid the warning about guessing the trace type, only to have my palette disappear.

Curiously, this behavior isn't present if everything is specified in the same call:

plot_ly(data = iris, x = ~Sepal.Length, y = ~Sepal.Width, color = ~Species, colors = "Blues")
plot_ly(data = iris, x = ~Sepal.Length, y = ~Sepal.Width, color = ~Species, colors = "Blues", type="scatter")

both return

Is colors the correct way to pass a palette to a specific layer? In other places it seems like it's actually colorspace? I know scatter doesn't have a colors argument in schema() (e.g. #1699) but clearly it's working when the type is inferred and I would like to provide a palette...

iris を使って 2 つの plot_ly/add_trace の例を再現し、生成されたパレットを比較します。plot_ly と add_trace のエントリポイント、特に明示的な type="scatter" パスにおける色の処理を追跡します。両方の呼び出し形式が一貫して colors="Blues" を受け入れ、異なる例に対する回帰テストのカバレッジがあることを完了条件とします。