If you only have a single product with RGB such as PC case fans, or maybe just a few items from the same manufacturer, it could be worth trying their RGB software ... the exact color you want.

introduces TT RGB PLUS 2.0, an all-in-one software that can integrate all the other software from your Thermaltake Fans, Liquid Coolers, Power Supplies and Memory, to bring integration ...

When you need to quantify the color of an object ... OpenCV at the problem and approach it through software, or you can buy an off-the-shelf RGB sensor and wire it up to an Arduino.