Check out the link below for coleus varieties in the color(s) you are looking for. Artemesia 'Limelight ' might be a good choice, too. Also, you might introduce a 3rd color and choose a coleus or other foliage plant w/all three colors in the leaf.

Here is a link that might be useful: coleus finder photos page

The perennials that come to mind for me that have a yellowish foliage are all too fine textured, or too tall. Looking at your picture though I wondered if you'd considered a burgundy foliage such as sedum 'vera jameson' It might be very pretty. I like the suggestion of using some of the sun coleus to tie it together if you introduce a new color.

I love yellow, white and blue all together as well. I have a yellow rose, a shasta daisy, Moonbean and larkspur. Last year I had the yellows and nastrushams. Talk about a riot of color!!!
There's soooo many new annuals out there, so taking a stroll through a good nursery will surely catch your eye and give you something really fun. Some of the new snapdragons are wonderful. The newer zinnias. Wow! Add some lobelia and you would have a great display.

heuchera?

I have a very similar corner with regular liriope, and coreopsis rosea. I have bergenia with them, but my spot never gets real dry. I'm wondering how dry bergenia can handle?