ANSI Escape Sequence

Text|Foreground: ESC[38;5;{index}m
Fill|Background: ESC[48;5;{index}m

Lua

function textColor(index)
	return '\27[38;5;' .. index .. 'm'
end

function fillColor(index)
	return '\27[48;5;' .. index .. 'm'
end

io.write(fillColor(4) .. textColor(12) .. 'bright blue text on blue background')

256 Color Index Chart

Windows Console