isDark static method
Returns true or false if the calculated relative luminance from the given hex
is less than 0.5.
Implementation
static bool isDark(String hex) {
var bC = basicColorsFromHex(hex);
return calculateRelativeLuminance(
bC[BASIC_COLOR_RED]!, bC[BASIC_COLOR_GREEN]!, bC[BASIC_COLOR_BLUE]!) <
0.5;
}