Custom color scales with rgba values are broken

[tbreloff]

Adjusting one of your examples:

var trace1 = {
  y: [5, 5, 5, 5],
  mode: 'markers',
  marker: {
    size: 40,
    colorscale: [[0,'rgb(255,0.0,0.0)'], [1,'rgba(0.0,0.0,255,0.5)']],
    color: [0, 1, 2, 3]
  }
};

var data = [trace1];

var layout = {
  title: 'Scatter Plot with a Color Dimension'
};

Plotly.newPlot('myDiv', data, layout);

The 2nd color of the colorscale is black if I try to use an rgba... why? Is there a way to get this functionality?

[etpinard]

Looks like you found a bug. Thanks for reporting 🍻

With the colorbar on, this issue is even more evident: http://codepen.io/etpinard/pen/zqqeBJ

[etpinard]

Here's the reason why: d3/d3#582

We have two options:

• write our own interpolate to handle rgba colours
• explicitly not allow rgba colours in custom colorscales. The alpha colours would be stripped out in is_valiid_scale_array.js

[tbreloff]

Well I think you know which option I would prefer ;)

The visualization that prompted this is a scatter where the markers get less transparent through time, giving an idea of how the distribution changes. I currently have to hack around the colorscale rgba limitation by sending a full list of rgba values for every data point.

Here's a toy example in Julia with Plots.jl (plotly backend):

[mdtusz]

Fixed in #422.