Personally, my opinion is that adding color seems to detract from the overall serious tone of the game, as well as the cold, gritty, technopunk aesthetic.
Final Fantasy IX was less serious, and overall more vibrant in aesthetic and tone, so colored icons worked there. FF's VII and VIII just don't have the right mood for it; My opinion.
The contrast and such may be tweaked and may even produce better looks afterward, but I made the icons as close to the originals (without pixeling each by hand) as possible.
On another note, the coloring doesn't look bad from a technical standpoint. In fact the color choice on a few of them is impeccable, and rivals such that I would use if I were to color them.
Essentially, your work isn't bad, I just feel it doesn't fit.