Vinca Major..the larger periwinkles. Bloomed like crazy for me until the first hard freeze last year. No dead-heading required, and blooms are very colorful and bright. My periwinkles were volunteers..showed up in my planter one day. I didn't plant them there. Soil in the planter is very poor. I never amended the soil yet the periwinkles thrived. Mine hated sun. I've heard people say that this vinca does well in sun....no it doesn't, not in my case. Mine would shrivel a bit in the afternoon when it got about an hour of full sun on its foliage. But they'd bounce right back once the sun was off of them. They should do fine for you in the planter in full shade. And they can get tall, so should be easy to see from a distance and won't vanish in the planter.

I have the same issue; thanks for posting, y'all! I'm gonna try some periwinkle in my shaded-by-the-house bed.

BTW, someone at this website says there are two kinds of periwinkle (annual and perienniel) and one likes full sun and the other full shade.

Here is a link that might be useful: Periwinkle

It is treated as an annual in some areas where the winter is harsh. It is a tender perennial and if not planted in a protected area frost will kill it. Mine dies back every winter but is always growing again by early summer.
I believe the Vinca (Periwinkle) in my planter is Madagascar Periwinkle. It is an upright plant that grows to approx. 1-2 feet tall, has bright fuschia pink blossoms, and it does not tolerate strong, direct sunlight. I don't know how it got in my planter ( I didn't put it there) and I've never seen it offered at the local nurseries. The only Vinca I've seen offered locally is the trailing, groundcover variety..Vinca Major (larger leaves) and Vinca Minor (small leaves, prefers shade).
Either of these would do ok in the planter box but nobody would be able to see them from a distance as they are trailing plants...they are prostrate and spreading, not upright.

So my suggestion is to look for Madagascar Periwinkle. If you purchase some of this plant, water and fertilize sparingly...keep the soil a bit on the dry side.