How about looking at variegated foliage, evergreen, low-growing shrubs with contrasting shaped foliage. I have a golden fastigiate yew tree which is very slow growing and is a beacon of gold throughout the year? Spotted Aucuba is another tough possibility, it would need to be kept under control size wise though.
@Keith-16 There are some good ideas on the Saga website as mentioned by @AnniD. Getting colour into a sunless border is difficult. Most annuals love full sun.Different coloured leaves would be best with the cotoneaster as a back drop.
I have worked as a Gardener for 24 years. My latest garden is a new build garden on heavy clay.
Unfortunately, you would probably not get outstanding colour because variegated leaves need sun and light to produce their best colours but at least the bed would not just be green. My yew tree is definitely more greeny yellow on its shady side, it is growing in full sun so bright gold on the sunny south side. A flat growing, miniature. golden conifer could spread over the edge of the wall to soften the hard edges. Do not be tempted by dwarf conifers, they can grow very large. They are called dwarf compared to the normal huge size of "ordinary conifers" which can grow to humungeous sizes and spreads. There is a definite difference between dwarf and miniature in the horticultural world.
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That would be good for colour - good idea
My yew tree is definitely more greeny yellow on its shady side, it is growing in full sun so bright gold on the sunny south side. A flat growing, miniature. golden conifer could spread over the edge of the wall to soften the hard edges. Do not be tempted by dwarf conifers, they can grow very large. They are called dwarf compared to the normal huge size of "ordinary conifers" which can grow to humungeous sizes and spreads. There is a definite difference between dwarf and miniature in the horticultural world.