Returns the RGB equivalent of the given HSV data, or vice-versa. Adapted from http://www.cs.rit.edu/~ncs/color/t_convert.html

HSVtoRGB.lua

function HSVToRGB( hue, saturation, value )
	-- Returns the RGB equivalent of the given HSV-defined color
	-- (adapted from some code found around the web)

	-- If it's achromatic, just return the value
	if saturation == 0 then
		return value;
	end;

	-- Get the hue sector
	local hue_sector = math.floor( hue / 60 );
	local hue_sector_offset = ( hue / 60 ) - hue_sector;

	local p = value * ( 1 - saturation );
	local q = value * ( 1 - saturation * hue_sector_offset );
	local t = value * ( 1 - saturation * ( 1 - hue_sector_offset ) );

	if hue_sector == 0 then
		return value, t, p;
	elseif hue_sector == 1 then
		return q, value, p;
	elseif hue_sector == 2 then
		return p, value, t;
	elseif hue_sector == 3 then
		return p, q, value;
	elseif hue_sector == 4 then
		return t, p, value;
	elseif hue_sector == 5 then
		return value, p, q;
	end;
end;

RGBtoHSV.lua

function RGBToHSV( red, green, blue )
	-- Returns the HSV equivalent of the given RGB-defined color
	-- (adapted from some code found around the web)

	local hue, saturation, value;

	local min_value = math.min( red, green, blue );
	local max_value = math.max( red, green, blue );

	value = max_value;

	local value_delta = max_value - min_value;

	-- If the color is not black
	if max_value ~= 0 then
		saturation = value_delta / max_value;

	-- If the color is purely black
	else
		saturation = 0;
		hue = -1;
		return hue, saturation, value;
	end;

	if red == max_value then
		hue = ( green - blue ) / value_delta;
	elseif green == max_value then
		hue = 2 + ( blue - red ) / value_delta;
	else
		hue = 4 + ( red - green ) / value_delta;
	end;

	hue = hue * 60;
	if hue < 0 then
		hue = hue + 360;
	end;

	return hue, saturation, value;
end;

HSVtoRGB.lua line 7 should be return value, value, value