rveciana - spam-js-with-authomatic-color-selection
spam.js with authomatic color selection

Based on this Martín González’s block, shows how to properly select the colours taking the neighbours in account as in this other block, which is based on this other one by Jason Davies!
<!DOCTYPE html>
<meta charset="utf-8">

<body>
<script src="http://d3js.org/d3.v3.min.js"></script>
<script src="http://d3js.org/d3.geo.projection.v0.min.js"></script>
<script src="http://d3js.org/topojson.v1.min.js"></script>
<script src="spam.js"></script>
<script src="rbush.min.js"></script>
<script>

var width = 960,
    height = 600

var i = 0

var color = d3.scale.category20()

var graticule = d3.geo.graticule()

// Canvas radial gradient
var x = width / 2,
    y = height / 2,
    // Radii of the start glow.
    innerRadius = 220,
    // Radii of the end glow.
    outerRadius = 300,
    // Radius of the entire circle.
    radius = 200

d3.json("world-50m.json", function(error, d) {
    topojson.presimplify(d)
    
    var neighbors = topojson.neighbors(d.objects.countries.geometries)
    var countries = topojson.feature(d, d.objects.countries)
    countries.features.forEach(function(d, i) {
          d.properties.color = d3.max(neighbors[i], function(n) { return countries.features[n].properties.color; }) + 1|0
          });

    var map = new StaticCanvasMap({
        element: "body",
        width: width,
        height: height,
        projection: d3.geo.orthographic()
            .clipAngle(90)
            .precision(0.1)
            .scale(250),
        data: [
            {
                features: countries,
                static: {
                    prepaint: function(parameters) {
                        parameters.context.beginPath()
                        parameters.path({type: "Sphere"})
                        parameters.context.lineWidth = 2
                        parameters.context.strokeStyle = "rgb(198, 197, 197)"
                        parameters.context.stroke()

                        var gradient = parameters.context.createRadialGradient(x, y, innerRadius, x, y, outerRadius)
                            gradient.addColorStop(0, 'rgb(248, 248, 248)')
                            gradient.addColorStop(1, 'rgb(210, 210, 210)')
                        
                        parameters.context.fillStyle = gradient
                        parameters.context.fill()

                        parameters.context.beginPath()
                        parameters.path(graticule())
                        parameters.context.lineWidth = 0.2
                        parameters.context.strokeStyle = 'rgba(30,30,30, 0.5)'
                        parameters.context.stroke()
                    },
                    paintfeature: function(parameters, d) {

                        parameters.context.lineWidth = 0.8 / parameters.scale
                        parameters.context.strokeStyle = "rgba(0,0,0, 0.6)"
                        parameters.context.stroke()

                        parameters.context.fillStyle = color(d.properties.color)
                        parameters.context.fill()
                    }
                }
            }
        ]
    })
    map.init()
})
</script>