Yes: These may be more open and greener than you would like in that position. However, it's possible there are few, if any other options for reddish leaves on a dwarf hardy shrub in USDA 4. There are additional introductions of dwarf red Japanese barberry cultivars that have more deeply colored leaves and other enhancements. Despite this species being regarded as a pest in parts of eastern North America large wholesale nurseries continue to select new cultivars and produce these in quantity. One or two of the dwarf red ones have been found to not fruit much.

I have a Crimson Pygmy barberry in west-facing part shade. It is not green or open at all, and does not flower, therefore does not set fruit. Be careful when weeding around them, they bite! They also have a tendency to collect garbage, so maybe aren't the best choice for a windy corner. Other than that, they're very low maintenance, nice orange fall color.

West-facing here is afternoon sun, unless something is between the sun and the face. Plenty of light for foliage color development, in fact way too much sun for plants requiring partial shade.

I have a Crimson Pygmy barberry in west-facing part shade. It is not green or open at all, and does not flower, therefore does not set fruit. Be careful when weeding around them, they bite! They also have a tendency to collect garbage, so maybe aren't the best choice for a windy corner. Other than that, they're very low maintenance, nice orange fall color.

Oops, sorry for the double post. bboy, you crack me up. The area the barberry is planted is in part shade, because there is a tree on the parkway to one side of the berm it is planted on. But the orientation is west. Maybe they stay greener in Seattle, everything seems greener there, but they don't seem to require high light to get that deep red color here, and they stay dense and compact. Rose Glow barberry, on the other hand, requires a little more light to get the pink variegation, it is also a larger shrub.

I have a Ruby Glow Barberry that gets shade all day accept about 2 to 3 hours in midday. It has lovely color and does well there. You might want to look for other purple leaved plants too. Midnight Wine Weigela comes to mind. Also Purple Pixie Loropetalum (probably not hardy for you?). It would be pricey, but one of the Dwarf red Japanese Maples would be a good choice for your conditions. Then there is Crinum Sangria. It's a bulb and might not be hardy, but likes shade and has purple foliage.

That's probably 'Rose Glow' barberry. If hardy in Zone 4 purple-leaved weigela is another group where small and purple cultivars are fairly easily found in outlets, that's true. But like other purple-leaved deciduous shrubs these are affected by the light exposure.

Crinums are all tender, even the most hardy ones like C. x powellii may be lost to hard winters here in Zone 8.

Weigela 'Midnight Wine' will stay small, while "Wine and Roses' will be larger and more floriferous. I THINK they are hardy for you, but am not sure, so apologize in advance if they are not.

Yes, indeed, it is Rose Glow barberry. I just hate it when my brain says one thing and my mouth (or in this case, my hands) say something else entirely! Ah....middle age. :)