[BUG]: The `quiver` trace ignores a discrete `marker.color` array and results in every arrow being black

[camdecoster]

Description

The quiver trace ignores a discrete marker.color array. Every arrow ends up black instead of taking its per-point color. A numeric array with a colorscale works, and a single color string works.

Screenshots/Video

No colorscale (the bug)	With colorscale (for comparison)

Steps to reproduce

• Open plotly devtools
• Run the following snippet in the browser devtools console

   Plotly.newPlot(gd, [{
     type: 'quiver',
     x: [1, 2, 3], y: [1, 2, 3],
     u: [1, 1, 1], v: [0, 1, 0],
     marker: { color: ['rgb(23, 103, 194)', '#FF4136', '#2ECC40'], line: { width: 3 } }
   }]);

• Note that all three arrows are rgb(0, 0, 0) (by inspection of using your eyes)
• Run the following modified snippet:

   Plotly.newPlot(gd, [{
     type: 'quiver',
     x: [1, 2, 3], y: [1, 2, 3],
     u: [1, 1, 1], v: [0, 1, 0],
     marker: { color: [0, 5, 10], line: { width: 3 } },
     colorscale: 'Viridis'
   }]);

• Note that the arrows have the correct color

Notes

• marker.color is documented as arrayOk, so the black arrows seem to be a rendering bug (rather than an unsupported input)
• Per the schema, each arrow should be drawn as its own color from the array. If this behavior is intentional, we should update the description.
• This was found while working on [BUG]: scattergl with a discrete string array marker.color logs "Invalid color specifier" and blackens hover/legend color (regression in v4) #8025