Pieris andromeda and Leucothea are two excellent choices with the added feature that they are not on the favorite food for the four-legged vermin

My zone's frost-free so forgive any errors in hardiness:

-heuchera, tiarella, hosta
-(groundcovers) oxalis siliquosa 'Copper Glow' (red tones) or 'Sunset Velvet' (coral tones), or Oxalis purpurea 'Grand Duchess' (purple black leaves). I have 'Sunset Velvet' and it's gorgeous to set off taller plants, easy to keep in check and doesn't reseed itself around.
-hellebores
-Rhaphiolepsis indica, Indian Hawthorn, has several dwarf forms, all have lovely pink flowers and blue-black berries; evergreen.
-dwarf coleonema: one has green foliage and very pale pink flowers; the other has yellow-gold foliage and white flowers

4 hours of late morning sun would constitute a part-sun in my garden. :-)
Anyway, for the spring interest any Azaleas or Rhododendrons will work. They vary in sizes and colors, so your choices are virtually endless. In your zone Satsuki hybrids azaleas are hardy and could provide main attraction in Spring with their bi-/tri-colored flowers.
For the mid-late season 'Edward Goucher' Abelia will provide you with very fragrant lavender/pink flowers from late July till November. Very pleasing fountain shape small shrub. Though is not completely evergreen, in mild winter it may stay evergreen. In my zone it loses its leaves around Christmas or so. 4 hours is more than enough for it to bloom.
As perennials goes, Astilbes should do great there if adeqate moisture provided.