function gray(value, delimiter) {
            return [value, value, value].join(delimiter || '');
        }
#Description:
===============================================
Generate random color value base on color type:
-> hex
-> rgb
-> rgba
-> 0x
-> named color

#Examples:
===============================================
* Geerate random hex color
chance.color() => '#79c157' / 'rgb(110,52,164)' / '0x67ae0b' / '#e2e2e2' / '#29CFA7'

* Generate Hex based color value
chance.color({format: 'hex'})    => '#d67118'

* Generate simple rgb value
chance.color({format: 'rgb'})    => 'rgb(110,52,164)'

* Generate Ox based color value
chance.color({format: '0x'})     => '0x67ae0b'

* Generate graiscale based value
chance.color({grayscale: true})  => '#e2e2e2'

* Return valide color name
chance.color({format: 'name'})   => 'red'

* Make color uppercase
chance.color({casing: 'upper'})  => '#29CFA7'

* Min Max values for RGBA
var light_red = chance.color({format: 'hex', min_red: 200, max_red: 255, max_green: 0, max_blue: 0, min_alpha: .2, max_alpha: .3});

@param  [object] options
@return [string] color value