I don't know of a Ceanothus 'blue star' and Google doesn't either - there is one called dark star though.
When you say you want it to 'cover' a fence, these plants are freestanding shrubs, though they prefer the shelter of a wall or fence behind them - they also like a sunny, reasonably sheltered spot, and any of the varieties will do, you just need to decide whether you prefer evergreen or deciduous, what height and spread you want, and whether you want one with dark blue, tight flowerheads, or looser, paler blue heads later in the year.

If you choose a few different varieties you can have various shades of blue. 'Puget Blue' is a lovely dark blue and 'Gloire de Versailles' flowers in autumn. Don't try to prune them as they don't like it!