Experts and BHG readers answer.
Planting in wet areas
A situation with wet soil in shade is not the best for growing colorful plants and flowers. However this is an ideal place to make interesting with all sorts of different leaf textures and colors. Consider growing astilbes and ferns with delicate lacy leaves alongside some bold-leaved ligularias (or hostas if it's not too wet). Add some damp-loving rushes or sedges for a vertical accent. Coleus provide good leaf colors except in standing water. Houttuynia cordata 'Chameleon' is another that will relish your conditions. Its heart-shaped leaves are irregularly variegated with green, cream, and red. Be careful though it makes an excellent ground cover but may become invasive.
Another good plant for wet shade is variegated sweet flag (Acorus calamus 'Variegatus') which has spear-shaped leaves banded in cream. Its relative, dwarf sweet flag (Acorus gramineus) is also valuable. The cultivar 'Ogon' produces fans of grassy evergreen leaves variegated with chartreuse and cream.
If the soil is not prone to flooding, you will find that there is a large range of suitable plants, but few of these are flamboyantly colorful compared to those for sunny sites. Nonetheless there is a certain subtleness about damp shaded places that defy description.