Support 8 character hex color codes

[franxois]

Expected Behavior

I would like to define the backgroundColor with hex format and alpha value #RRGGBBAA
The graph should use this color, as well as the tootltip

Current Behavior

With chart.js 2.3.0
The graph bar use the good color but the console is flooded with errors
With chart.js 2.7.3
The graph bar use the good color but the tooltip is black

Possible Solution

Steps to Reproduce (for bugs)

With chart.js 2.7.3
https://jsfiddle.net/u1tykvqb/

Context

Environment

• Chart.js version:
• Browser name and version:
• Link to your project:

[benmccann]

Looks like backgroundColor is used to set the fillStyle: https://github.com/chartjs/Chart.js/blob/master/src/core/core.tooltip.js#L824

Hex looks to be a valid value for fillStyle. I suppose something must be breaking between taking the value and using it. https://www.w3schools.com/tags/canvas_fillstyle.asp

[benmccann]

This works on master (switch out the JS resource in the fiddle for https://www.chartjs.org/dist/master/Chart.min.js), but strangely the bars turn black when hovering. model.backgroundColor is sometimes rgb(0,0,0) in setHoverColor: https://github.com/chartjs/Chart.js/blob/master/src/core/core.datasetController.js#L287

[benmccann]

The fiddle is using an unrecognized color '#0081cdaa. Only 6 character hex codes are supported

[benmccann]

Support is missing from https://github.com/chartjs/chartjs-color-string. It's supported upstream, but we forked the code before support was added

[benmccann]

I sent a fix: chartjs/chartjs-color-string#4

[simonbrunel]

I think it's a duplicated of #5152, which already have an opened PR that we should try to get merged.