Lilacs! When I read dwarf, I thought you wanted something about a foot tall. If so, you might consider Iberis. It does need to be cut back hard after bloom to keep it from getting woody and rangy, but it's evergreen and a great small shrub.

What exactly do you mean by a "dwarf shrub"? How tall.

Do you flowering or year round color? Do you want something you will shear like boxwood?

SOme weigelia have purple leaves, black lace elderberry,
purple pavement roses, PJM rhodemdron (sp?), barberries (nice puprle foliage but no flowers),.. juzf zoms fhoughts..
you can get color in different ways than flowers..

Lynn