I'm currently in love with the toxicologist color, viridian green.
Blademaster's Mauve, Aetherial Blue and Transliminal Violet are fantastic because of the way they change color based on material & lighting.
Still love the good old daedric red / coldharbour ash black combo, even though it has been superceeded by cyrodillic steel / blademaster's mauve for me.
Coldharbour Ash Black because it's one of the few that actually work properly. Most others are strongly affected by the armor and don't look remotely the right color.