Each media should be calibrated on it's own to mach certain colors. One media will have a different white point then another media. Which will change the color of your print slightly. I would look into some color management programs. Their are colors that cause issues with this machine but not really green. Mostly greys, oranges, reds. The L25500 should be able to hit almost any color you need. But it needs to be profiled for the media correctly. There is no easy use these rendering intents and use this heat and passess etc. One thought might be that you are trying to use to little passes in hopes of saving ink. This will dramatically lower your gamut and the strength of your colors.