I experimented with colour in the beginning but decided I like black best. I think I preferred Blitz&Glitz Fluidline though, so I will go back to that when my Blacktrack runs out.
I have not tried the Guerlain stuff but it does look very nice and good reviews! The blue might be quite nice as blue makes my brown eyes really stand out. Will have a look next time I go shopping! (God knows when that will be :()