Ok, dogwoods are good choice.....but go for yellow leaved variety, Aurea. And green and white variety, Elegantissima. You get foliage colour in summer and those red stems from autumn to spring. Cut them bard back in spring.
You gotta have hellebores......try to get some mushroom compost in the planting holes. Range of colours from white to yellow to red to pink, sIngle and double flowers and evergreen lush foliage.
Test your soil.....see if it's acid or alkaline. This is easy amd cheap to do but essential. When we know what your soil is we can suggest the right sort of shrubs. For example hydrangeas would look good there but if your soil is acid go for a blue variety. If soil is alkaline go for a red variety.
Look to foliage for colour too. Heucheras look good over winter with fantastic evergreen foliage, blue grass elymus magellanicus is a brilliant metallic blue colour, acorus Ogon is an evergreen yellow "grass" and ophiopogon nigrescens is an evergreen black "grass. Campanula dicksons gold makes a yellow evergreen mound. Carex buchanii is a foxy red coloured upright evergreen grass. How about winter flowering heathers? They flower in winter and many have coloured foliage too. Phormiums are grass like plants in evergreen reds, yellows and greens and make impressive structural impact. Could go on forever but euphorbias are good too......some have evergreen purple/red foliage, some green and white foliage and they have yellow spring flowers too. Loads to consider for a brilliant winter garden