public void setYearDigitCount(int yearDigitCount) {
        if (yearDigitCount < 0 || yearDigitCount > 4) {
            throw new IllegalArgumentException("yearDigitCount cannot be smaller than 0 or greater than 4");
        }
        this.yearDigitCount = yearDigitCount;
    }
Color when month is before the current selected month
library/src/main/java/com/github/badoualy/datepicker/MonthView.java