Backyardgardener makes some great points.* With those in mind some plants could be:
Caladium - lovely patterned leaves for shade to part sun, these bulbs can be dug and replanted yearly.* They will need to be dug and stored each winter before a frost.* These sites will give you ideas of the leaf shapes and colors.* The first site has some great growing and planting tips.
You could surround them with Impatiens wallerana.* I would think just a couple of caladium bulbs and maybe 3 impatiens per pot.*
New Guinea impatiens (Impatiens x hawkeri) has larger flowers and patterened leaves.* I find it will tolerate more sun then the ones above.
Toreniafournieri aka wishbone flower will make a nice drooping mound in part sun.* I prefer the dark purple variety.
Fuchsia also does well in part sun.* There are many varieties of brightly colored flowers.* My favorite is Fuchsia 'Gartenmeister' with it's bright orange/red tubular flowers.* I bring the plants indoors for the winter and take cuttings in February to start new plants for the spring.* It has dark green* leaves with a tinge dark purple veins and would look great with your colors.* I think there are 2 or 3 in the large planter in the second pic.
Maybe this will give you more ideas.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.