How to pick color palette for a pie-chart? [closed]

Question

I have some code that generates image of a pie chart. It's a general purpose class, so any number of slices can be given as input. Now I have problem picking good colors for the slices. Is there some algorithm that is good at that?

Colors need to follow some rules:

• they need to look nice
• adjacent colors should not be similar (blue next to green is a no-go)
• pie background color is white, so white is out of option

Some algorithm manipulating with RGB values would be a preferred solution.

Answer 1

I solved it as follows:

1. Choose a base color.
2. Calculate its hue (baseHue).
3. Create a color with the same saturation and luminosity, with its hue calculated as:

     hue = baseHue + ((240 / pieces) * piece % 240
   

In C#:

int n = 12;

Color baseColor = System.Drawing.ColorTranslator.FromHtml("#8A56E2");
double baseHue = (new HSLColor(baseColor)).Hue;

List<Color> colors = new List<Color>();
colors.Add(baseColor);

double step = (240.0 / (double)n);

for (int i = 1; i < n; ++i)
{
    HSLColor nextColor = new HSLColor(baseColor);
    nextColor.Hue = (baseHue + step * ((double)i)) % 240.0;
    colors.Add((Color)nextColor);
}

string colors = string.Join(",", colors.Select(e => e.Name.Substring(2)).ToArray());

I used the HSLColor class.

The Google Charts example that uses 12 pieces and a base color of #8A56E2:

Answer 2

I would pre-compile a list of about 20 colors, then start repeating with the 2nd color. This way you won't break your second rule. Also, if someone makes a pie chart with more than 20 slices, they have bigger problems. :)

Answer 3

Take a look at Color Brewer, a tool that helps to define a coloring scheme to convey qualitative or quantitative information: maps, charts, etc. Out of three "types" of palettes that this tool can generate - sequential, qualitative, and diverging - you probably need the latter, diverging...

You can even download Excel files with RGB definitions of all the palettes.