Is this for the damp clayey meadow referred to in your other thread? If so, it will depend a whole big lot on HOW damp, and also depend on how wet it is in late winter early spring in particular.
If it is only "kinda" clayey and "kinda" damp, you might be able to grow some selected varieties of flowering crabapples, some of them are quite brightly colored. Or intelligently-selected ornamental plums or Canada plum. If also reasonably sheltered from wind and doesn't bake in summer, you might be able to grow witchhazel (certainly the fall-blooming one but its flowers are nearly invisible; but I'm speaking more of the slightly-less-hardy spring blooming ones, e.g. Arnold Promise)
If it is really pretty darn clayey and too damp for crabapples, you could still perhaps grow Bradford (ornamental) pears if they are hardy in your area (I forget, you'd have to look it up)
If you would accept bushes, a variety of Viburnums do well on damp clay and have large flat clusters of white flowers in late spring (around now, up here) although they do not stay in flower very long but some have noticeable berries in fall. Some of the Viburnums can get pretty big. Likewise with elders, which are even more moisture-tolerant. Also lilacs can be reasonably clay-tolerant tho they won't take real damp conditions.
Honestly though, "damp heavy clay" and "flowering woody plants" and "zone 5" are not things that go together well, sorry. You may have to look more to foliage color if you want colorful trees, or *flowers* for color.