Hi Martin
I am already an OH3 and configure everything via UI but the link below, with some modifications, is working for me and should work also in OH 2.5.10.
This is my code, adjust the JSON.stringify to your Device and use it as JS Output Transformation
(function(i) {
var sRGB = input.split(',');
//sR, sG and sB (Standard RGB) input range = 0 ÷ 255
//X, Y and Z output refer to a D65/2° standard illuminant.
var sR = sRGB[0];
var sG = sRGB[1];
var sB = sRGB[2];
var var_R = ( sR / 255 );
var var_G = ( sG / 255 );
var var_B = ( sB / 255 );
var_R = Math.pow(var_R, 2.19921875);
var_G = Math.pow(var_G, 2.19921875);
var_B = Math.pow(var_B, 2.19921875);
var_R = var_R * 100;
var_G = var_G * 100;
var_B = var_B * 100;
var X = var_R * 0.7161046 + var_G * 0.1009296 + var_B * 0.1471858;
var Y = var_R * 0.2581874 + var_G * 0.7249378 + var_B * 0.0168748;
var Z = var_R * 0.0000000 + var_G * 0.0517813 + var_B * 0.7734287;
var x = Math.round((X/100)*65534);
var y = Math.round((Y/100)*65534);
var payload = {};
payload.Color = (x + "," + y);
return JSON.stringify({ "Device": "0x0F6C", "send": payload });
})(input)