Function to PostgreSQL to Calculate Lighter or Darker Hex Colors.

ColorLuminance.sql

--
-- Convert to decimal and change luminosity
-- Inspired by: http://www.sitepoint.com/javascript-generate-lighter-darker-color/
--
--

-- Reverse: to_hex
-- See: http://grokbase.com/t/postgresql/pgsql-general/0541qyk9ya/help-with-converting-hexadecimal-to-decimal
CREATE OR REPLACE FUNCTION from_hex(t text) RETURNS integer AS $$
DECLARE
	r RECORD;
BEGIN
	FOR r IN EXECUTE 'SELECT x'''||t||'''::integer AS hex' LOOP
		RETURN r.hex;
	END LOOP;
END
$$ LANGUAGE plpgsql;


CREATE OR REPLACE FUNCTION ColorLuminance(cor VARCHAR, lum FLOAT) RETURNS TEXT AS $$
DECLARE
	cor ALIAS FOR $1;
	lum ALIAS FOR $2;
	hexa TEXT;
	c FLOAT;
	i INTEGER := 0;
	aux TEXT  := '';
	rgb TEXT  := '#';
BEGIN
	
	
	SELECT regexp_replace(cor, '[^0-9a-f]', '', 'gi') INTO hexa;

	IF cor = 'transparent' THEN
		RETURN 'transparent';
	END IF;

	IF (length(hexa) < 6) THEN 
		SELECT CAST( (substr(hexa, 1, 1) || substr(hexa, 1, 1) || substr(hexa, 2, 1) || substr(hexa, 2, 1) || substr(hexa, 3, 1) || substr(hexa, 3, 1)) AS VARCHAR) INTO hexa;
	END IF;
	
	FOR i IN 0..2 LOOP
		SELECT from_hex(substr(hexa, (i*2+1), 2)) INTO c;
		SELECT to_hex(CAST(LEAST(GREATEST(0, c+(c*lum)), 255) AS INTEGER)) INTO aux;
		SELECT (rgb || substr('00' || aux, length(aux)+1)) INTO rgb;
	END LOOP;

	RETURN rgb;
	
END;
$$ LANGUAGE plpgsql;


--select ColorLuminance('#69c', 0);	-- returns "#6699cc"
--select ColorLuminance('6699CC', 0.2);	-- "#7ab8f5" - 20% lighter
--select ColorLuminance('#69C', -0.5);	-- "#334d66" - 50% darker
--select ColorLuminance('00', 1);	-- "#000000" - true black cannot be made lighter!