... Puzzle why all the colors look so good except the 900's green.
It is an interesting phenomenon, hopefully some one with more knowledge will chime in with a suggestion on why that is happening.
Also of interest: three of the colors in the Marutt 4900 chart, are actually out of the printer's gamut with BC luster.u
Have you tried printing the green with ACPU?
You could also try experimenting with a green ramp and see if at some point it changes from green to black.
Brian A