Because the colour of Sombrieul is a beautfull cream, you could put any coloured clematis with it. It all depends on what look you want to create. As you know there are three types of clematis in regards to pruning. Because a rose has nasty thorns, it may be easier to plant a class where you just cut the clematis off at the bottom every year, such as the vitcella group. Plus you get more bang for your buck with this group as they produce a greater amount of flowers. Also the flowers are smaller and so don't overpower the rose blooms. Here are a few sugestions for this class of clematis. Etoile Violette...single deep purple with yellow stamens, Blue Angel...icy blue, petals look like crepe paper, Mme Julia Correvon...rich wine red and Ville de Lyon...carmine pink. All these will grow without a lot of trouble. If you have never grown clematis before, then try jackmanii Polish Spirit, it will grow if you just drop it on the ground. The colour is a rich royal purple.