Are you sure your clients are getting Bord of the colors?
see I thought about this myself with my clients, I came to the conclusion that it wasn't them getting Bord ... it was me lol ,
you see there wearing one color for 2 weeks , then changing it , while us (the techs ) are looking at wearing and doing treatments day in day out with all the colors , get my drift?
another thing I realized is that for 1 , these are 12 of the most used nail colors ever really aren't they?
bearing that in mind before I was a nail tech I had a huge collection of nail polish and you know what? out of all of them there was probably only 5 or 6 colors that I wore regally , so I believe the same with shellac,
another thing to consider would be the way you approach the treatment with the client, if your positive, confident and bigging it up they will be happy to go with it ,
if your down and negative or apologetic they will feed off that to ,
also once they have seen for them self's the effects and freedom of wearing shellac for several weeks on there natural nails I don't think the fact that there are only 12 colors will up set them to much
if all this fails then why not bling it a bit? add some stripes , a gem stone, a sprinkle of glitter, try alternative colored french ect.