defaultColors (colors) {
        if (!arguments.length) {
            // Issue warning if it uses _schemeCategory20c
            if (this._defaultColors === Config._schemeCategory20c) {
                logger.warnOnce('You are using d3.schemeCategory20c, which has been removed in D3v5. ' +
                    'See the explanation at https://github.com/d3/d3/blob/master/CHANGES.md#changes-in-d3-50. ' +
                    'DC is using it for backward compatibility, however it will be changed in DCv3.1. ' +
                    'You can change it by calling dc.config.defaultColors(newScheme). ' +
                    'See https://github.com/d3/d3-scale-chromatic for some alternatives.');
            }
            return this._defaultColors;
        }
        this._defaultColors = colors;
        return this;
    }
Set the default color scheme for ordinal charts. Changing it will impact all ordinal charts.

By default it is set to a copy of
`d3.schemeCategory20c` for backward compatibility. This color scheme has been
[removed from D3v5](https://github.com/d3/d3/blob/master/CHANGES.md#changes-in-d3-50).
In DC 3.1 release it will change to a more appropriate default.

@example
config.defaultColors(d3.schemeSet1)
@param {Array} [colors]
@returns {Array|config}