How about some winter pansies and trailing ivy or some of the winter flowering heathers.

If you click on 'W' at the bottom of the page, you'll find 'Winter container ideas'. That might help you.

Pansies buy them in the autumn when flowering, Primulas, Snowdrops, Chinidoxia, dwarf Narcissus such as little gem, dwarf Iris, dwarf Tulips a slow growing evergreen shrub, trailing Ivy, I dont feed and never need to water in the winter months.