Bonjour, Danielle & Etsy neighbors!
I have been sort of passive about this. I have had many clients approach me with their specifics. For example, I've made several sets of table napkins, which were variations of dishtowels, in custom colorways. Brides who come to my shop are often very specific about their color palettes -- but I think that they are accustomed to approaching potential vendors with their preferences and are in general very clear about their visions/needs.
So your post got me thinking, too. I tend to wait to be asked. I think that this tendency is in keeping with my personality, and I'm not so sure it makes for good business. However, I am approached regularly by potential custom order clients, so I'm not completely off track (maybe people at custom order listings and/or feedback...)
More food for thought. Thanks for the virtual Parisienne pastry...