residual_plot: strange behavior of the color_by parameter

[ASmirnov-HORIS]

Current behaviour:

data = {
    "x": [0, 1, 0, 1],
    "y": [0, 1, 0, -1],
    "g": ["a", "a", "b", "b"]
}
residual_plot(data, "x", "y", color_by="g")

but I rather expect:

i.e. separated statistic for each group (= each color).