How is the colour coding decided for partial grouping of countries?

Three-colour coding is used to visualize partial grouping of countries by an indicator. According to the values of an indicator achieved by countries, they are divided into three groups of approximately equal size (terciles): the top third, the middle third and the bottom third. A distinct colour is attached to a group of countries with similar level of performance. The colour-coding scale graduates from darkest to lightest. The darker shade of green represents the top third group; the moderately shaded green represents the middle third; and the lighter shade of green represents the bottom third of countries. Partial grouping of countries applies to all indicators listed. Sex ratio at birth is an exception—countries are divided into two groups: the natural group (countries with a value between 1.04-1.07, inclusive), which uses darker shading, and the gender-biased group (all other countries), which uses lighter shading. When indicators are expressed as female to male ratio, countries with values in the vicinity of one are coloured as top performers in that indicator. Large gaps in favor of men are treated equally as those in favor of women. For some very skewed distributions (e.g., female primary school gross enrolment ratio and total unemployment rate, female to male ratio), the groups differ in sizes greatly. See Technical note 6 at http://hdr.undp.org/sites/default/files/hdr2016_technical_notes.pdf for details about colour coding in this table.