I would leave the planters as-is, and instead put a variety of plants in them. Use the thriller, filler, spiller technique: thriller plants add a vertical element and drama, filler plants are placed in front/around the thrillers, and are used to make the containers look full, and spillers hang over the edge of the planter to help soften the look.

Where are they? Front of house? Back? Side? What else is around them?

You could certainly mosaic them, tile them etc. You could even just paint them a stand out color but as suggested above why not make the foliage the star and plant them up a bit more showy.

I cannot imagine much being happy in those shallow planters but the plants in there look to be growing by some miracle . I would not tile those since they might actually be somehow breathing and thta is agood thing . Maybe at least show us where they are in relation to the house . Post the pics from further back in comments DO NOT start another post .

I want to keep the plants or add new plants but do something to the planter itself other than just plain white. This is in the backyard behind the pool.

Here are a few ideas:

Your photo is very deceiving since the main plant installed in the planters is the White Bird of Paradise which looks to be at least 3-5 ft. tall and easily grows in Florida to 25 ft in about 2 years. Those plants will never stay contained in that planter.

One could assume that the planters you have in this photo are 3 ft in height. I would consider painting them the same color as the patio area in which they reside.

I know you would like to do something with the planters as opposed to the plants, but the plants are meant to be the centerpiece when it comes to landscaping, so I would plant more colorful, eye catching foliage instead or in addition to the plants that you have.

I would explore having a pretty border tile around the top edge of each planter, and paint planters a complimentary color with tile. Consider the colors you want for that area.

If those planters were built properly and aren't showing signs of leaking, efflorescence or paint bubbling, then I would leave them alone and not mess with them at all. Not a fun thing to have to maintain!

You could also wrap vertical bamboo strips around them