The "In Series" option was available earlier, but for some reason it has been discontinued by UltraSabers. However, you can easily rewire that without getting power issues or whatsoever. You just need to splice an additional wire from the positive of the 4th channel of the Emerald Driver to the positive of the Amber LED. The same is done for the negative. That should give you the Amber LED back again.
Regarding luminescence or colour space...even without the 4th die you can produce any colour from the RGB spectrum and without a loss of luminescence. Amber can boost some of the orange and red shades, though, so rewiring that might be advantageous for you