Heuchera and hardy geraniums are very good and extremely reliable. The heuchera are evergreen so even in the middle of winter you still have leaves - which come in a variety of colours, from vivid lime green, to russet, to cherry red/purple and even black, they can make a stunning patchwork of colour.
The hardy geraniums are very robust and come back year after year, with a whole range of flower colours between bluey purple through to pink and even white.
They're both low growing, are relatively shallow rooted, and very hardy. Best of all they hardly require any work! Just a trimming back of dead leaves and tidying up every now and then.
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