Part of the problem is finding things that are small and bloom.
Here's my current go to plant
Mazus reptans, tolerates wet conditions but not submerged.
Lobelia cardinalis might be a good choice but they bloom only once a year.
The flowers are an intense cardinal red. I've got one that is budding up, when it blooms I'll post a pic.
Another good candidate would be Forget-me-Not, they like wet conditions and bloom on maturing plants but not sure how long they would bloom for. They also could get pretty big over time.
Search for groundcovers that tolerate wet conditions.