Here are some of my ideas.
You might think about 'Mint Julep'
These are the winter/springcolors. This winter it had burgandy red veins in it. Now it is turning all yellow. By summer it should be green. I bought this as a plug last fall. So it did winter over in the pot.
I lost the summer picture in my crash but it is in the data base here on all things plants. A very bright green with a silverish overlay.
This is 'Sugar Plum' A very large plant. Just bought this so no experience with growing
This is 'mocha mint' Has always be tough. These are 2 year old cuttings.
This is green spice, another work house of heucheras. Might look nice.
Last you might consider
Brunnera 'Looking Glass" very silver, this is the spring growth
These are plugs from last year.
No picture and I don't know what kind of sun the plants will get but there is a ghost fern tht is all gray. Sorry no picture. It stands about 18 inch high. Mine is 2 years old and in a pot so in the ground they may get bigger.