It's not evergreen: I have a deciduous azalea (yellow flowers) and a non-strident orange asiatic growing through the branches. As the azalea leafs up the fading lily is well-disguised.

A similar arrangement has developed between a Hamamelis and an asiatic, with a bit of help from a 'Sulphur Queen' Rhododendron.

Other possibles might be Pieris, Andromeda, Ericas because of the similarities in soil requirements.

good morning Seattle!
I have used Iberis sempervirens, perennial candytuft.
It grows well in the PNW and is not fussy.
It's white flowers go well with every Asiatic lily I've had so far.
GH

I don't know if this would work in Seattle. In fact, the verdit is still out for my garden here in NC. But, I planted yellow corydalis under my lilies. I got some nice color in the spring and I'm hoping the fern-like foliage will keep the lilies feet cool this summer and look good.

Shelley

Ferns

I've got mine in a bed with corydalis lutea, upright white phlox, and some striped hostas.