Sorry for necromancing this thread, but I'm really excited to find this! I've been slowly grinding away at a Warhammer High Elf-based Melnibonean army since the mid-1990's and just pulled it out again to convert to a Kings of War force.
I agree that the text doesn't give us much information on the military side of things other than the bronze armor and the color yellow. There is also some language that Elric was wearing yellow and gray early on in the first book, which suggests to me that those were some kind of royal colors. Beyond that, we get clues from Elric's black armor which I give to the Dragon Princes as well.
Beyond those clues, I have tried (with varying levels of success) to capture the sort of colorless pallette from the 60's and 70's book covers so the army "feels" right. But I'm also a big fan of the Dreaming City graphic novel, which depicts Melnibonean style as somewhat garish. So my approach has been yellow tunics, dark bronze armor, with muted but high contrast secondary tones (white, black, brown, gray) and the occasional brightly colored sash or feather (red, fuschia, wine, or pthalo green). I'll post pics if there is interest.