Posted: 13/12/2017 at 17:00
I agree about the viticellas but do also look at Princess Diana in the texensis group. She's a good strong grower with rich pink flowers that can go on for months. She does fine in full sun as the flowers don't fade - http://www.clematis.hull.ac.uk/new-clemdetail.cfm?dbkey=530 .
Betty Corning is pale lilac and has the added bonus of being perfumed - http://www.clematis.hull.ac.uk/new-clemdetail.cfm?dbkey=562
Blue Angel is good if you want more open flowers. Lilac, with a ruffle on the edge and a lovely darker bar on the reverse. http://www.clematis.hull.ac.uk/new-clemdetail.cfm?dbkey=88
Etoile Violette is superb too but can be too vigorous in some situations.
All of these are very hardy and, once settled, grow very well producing new stems each year so the display just gets better and better. Clematis like to be buried deeper than they were in their pot and are hungry, thirsty plants so if your soil is at all poor make sure you work in plenty of well-rotted manure and garden compost before planting. Keep them well watered in their first season as be patient. Sometimes they spend a year or so putting down their roots before they explode up top.
Try this nursery - https://www.hawthornes-nursery.co.uk/ they have a national collection of viticellas as well as a breeding programme for new selections. Richard, the owner, sometimes posts on here and is always happy to give advice.