Color of Contour lines in Surfaces with colormap are not correctly set

[jparisu]

I think there is an issue in the way the lines plot by a contours in a Surface object when selecting the color.
I think the color is not being correctly selected by each of the lines. They are supposed to follow the colorscale, but they just follows half of it.

Here there is a minimum example of code to simulate the error:

import numpy as np
import plotly.graph_objects as go

x = np.linspace(0, 1, 100)
y = np.linspace(0, 1, 100)
x_grid, y_grid = np.meshgrid(x, y)

z = x_grid + y_grid

params = {
    'colorscale': 'rainbow',
    'surfacecolor': z,
    'showscale': True,
    'colorbar': {
        'title': 'z',
    },
    'contours_z': {
        'show': True,
        'usecolormap': True,
        "project_z": True,
    }
}

trace = go.Surface(
    x=x,
    y=y,
    z=z,
    **params)

fig = go.Figure(data=[trace])
fig.write_image("test.png")
fig.show()

In the example, the expected behavior will be for the contour lines to be the same color as the surface, but they are not.

[jparisu]

I just realized the parameter surfacecolor is not needed, and removing it fixes the problem.
However, I still wonder why if z=surfacecolor the result is not the same as removing surfacecolor.

Update

Also, I am encountering some strange behavior, as if I remove surfacecolor I get the correct surface, but the parameter usecolormap from contours_z does not longer apply and the color of the lines is always the same when having 2 surfaces in the same plot (with only one as the example it seems like it does not happen).

[gvwilson]

Thanks for the bug report @jparisu - can you please post your note about strange behavior in our forum (https://community.plotly.com/) to see if someone there has a fix? (Realistically, it's going to be a while before we can look at it…) Thanks - @gvwilson