score:1

the idea then is to give a greener color (meaning it is more important), from a red to green color scale, to the skill that has higher percentage.

..., an ordinal scale is not the adequate choice.

You can use a linear scale with two colours in the range, "red" and "green", but the result is not nice. So, this solution uses three colours in the range: "red", "yellow" and "green".

The trick to do that is using three values in the domain:

``````var color = d3.scale.linear()
.domain([d3.min(pie_data, d => d.course_area_percentage),
d3.mean(pie_data, d => d.course_area_percentage),
d3.max(pie_data, d => d.course_area_percentage)
])
.range(["red", "yellow", "green"]);
``````

Here is a demo:

``````var pie_data = [{
"hard_skill": "Strategy",
"course_area_percentage": 9
}, {
"hard_skill": "Analytics",
"course_area_percentage": 18
}, {
"hard_skill": "Economics",
"course_area_percentage": 11
}, {
"hard_skill": "Finance",
"course_area_percentage": 7
}, {
"hard_skill": "HR",
"course_area_percentage": 5
}, {
"hard_skill": "Innovation",
"course_area_percentage": 2
}, {
"hard_skill": "International",
"course_area_percentage": 5
}, {
"hard_skill": "Marketing",
"course_area_percentage": 7
}, {
"hard_skill": "Operations",
"course_area_percentage": 14
}, {
"hard_skill": "Others",
"course_area_percentage": 11
}, {
"hard_skill": "Project",
"course_area_percentage": 11
}]
var width = 500,
height = 500,
radius = Math.min(width, height) / 2;

var color = d3.scale.linear()
.domain([d3.min(pie_data, d=>d.course_area_percentage),
d3.mean(pie_data, d=>d.course_area_percentage),
d3.max(pie_data, d=>d.course_area_percentage)])
.range(["red", "yellow", "green"]);

var arc = d3.svg.arc()

var pie = d3.layout.pie()
.sort(null)
.value(function(d) {
return d.course_area_percentage;
});

var svg = d3.select("body").append("svg")
.attr("width", width)
.attr("height", height)
.append("g")
.attr("transform", "translate(" + width / 2 + "," + height / 2 + ")");

var g = svg.selectAll(".arc")
.data(pie(pie_data))
.enter().append("g")
.attr("class", "arc");

g.append("path")
.attr("d", arc)
.style("stroke", "gray")
.style("fill", function(d) {
return color(d.data.course_area_percentage);
});

g.append("text")
.attr("text-anchor", "middle")
.attr("transform", function(d) {
return "translate(" + arc.centroid(d) + ")";
})
.attr("dy", ".35em")
.text(function(d) {
return d.data.hard_skill;
});

function type(d) {
d.population = +d.population;
return d;
}``````
``<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>``

As an alternative solution, if you want to use the color array you wrote in the question...

``````.range(["#008e15", "#3fe256", "#eef200", "#f19d00", "#d7191c"]);
``````

... you should use a quantize (or quantile) scale instead:

``````var color = d3.scale.quantize()
.domain(d3.extent(pie_data, d => d.course_area_percentage))
.range(["#d7191c", "#f19d00", "#eef200", "#3fe256", "#008e15"]);
``````

Here is the demo:

``````var pie_data = [{
"hard_skill": "Strategy",
"course_area_percentage": 9
}, {
"hard_skill": "Analytics",
"course_area_percentage": 18
}, {
"hard_skill": "Economics",
"course_area_percentage": 11
}, {
"hard_skill": "Finance",
"course_area_percentage": 7
}, {
"hard_skill": "HR",
"course_area_percentage": 5
}, {
"hard_skill": "Innovation",
"course_area_percentage": 2
}, {
"hard_skill": "International",
"course_area_percentage": 5
}, {
"hard_skill": "Marketing",
"course_area_percentage": 7
}, {
"hard_skill": "Operations",
"course_area_percentage": 14
}, {
"hard_skill": "Others",
"course_area_percentage": 11
}, {
"hard_skill": "Project",
"course_area_percentage": 11
}]
var width = 500,
height = 500,
radius = Math.min(width, height) / 2;

var color = d3.scale.quantize()
.domain(d3.extent(pie_data, d=>d.course_area_percentage))
.range(["#d7191c", "#f19d00", "#eef200", "#3fe256", "#008e15"]);

var arc = d3.svg.arc()

var pie = d3.layout.pie()
.sort(null)
.value(function(d) {
return d.course_area_percentage;
});

var svg = d3.select("body").append("svg")
.attr("width", width)
.attr("height", height)
.append("g")
.attr("transform", "translate(" + width / 2 + "," + height / 2 + ")");

var g = svg.selectAll(".arc")
.data(pie(pie_data))
.enter().append("g")
.attr("class", "arc");

g.append("path")
.attr("d", arc)
.style("stroke", "gray")
.style("fill", function(d) {
return color(d.data.course_area_percentage);
});

g.append("text")
.attr("text-anchor", "middle")
.attr("transform", function(d) {
return "translate(" + arc.centroid(d) + ")";
})
.attr("dy", ".35em")
.text(function(d) {
return d.data.hard_skill;
});

function type(d) {
d.population = +d.population;
return d;
}``````
``<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>``