If i use 0.8 Threshold, this will remove more than red pixels. if i set lower than 0.8 , nothing happens , is still red.
Of course, with RED background you will loose all pixels with red component. For keying always used color, which have big contras with main colors. In your case you must use BLUE color for background. And i don’t understand why you use this? You can easy create image with alpha channel or transparency in any 2D programs, save to PNG or TGA and use it. Because a Chroma Key used for create transparency in Render Target and expensive for mobile platforms.