Popsicle-colored impatiens (red, hot pink, violet, orange) make Halcyon "pop." They do the same for yellow hostas, and green hostas, and variegated hostas....
~Bunnycat

I have Heuchera 'Plum Pudding' and Acer palmatum dissectum 'Tamukeyama' in my bed with Halcyon with some other green plants. Also, Dicentra 'Ivory hearts' has some nice blue-green foliage that repeats the Halcyon color nicely. However, its kinda slow growing, so I'm not sure sure yet if it will work out. How about some blue and green variegated hostas too to tie it all together?

I like stuff like Hosta Guacamole with halcyon...or/and lychnis coranirus ( or however it's spelled) and lamium white Nancy.
Linda C

Year before last I put a large container behind halcyon to fill a hole and threw in some left over annuals. One was a chartruse sweet potatoe vine which draped over the halcyon. Turned out to be a great combination, each showing the other off.

Pulmonaria 'Opal' or 'Trevi Fountain', after flowering grow long very dark green leaves with widely spaced silver splotches. They contrast nicely with Halcyon. Hosta 'Revolution' has pale yellow centers, nice dark green margins. Very pleasing together to my eye in my garden. Dream Weaver, Dream Queen, and Thunderbolt also are dark green and yellow centered. They get large, eventually (slow growers).

~Bunnycat

Heuchera 'Lime Rickey' PP16210 EU17451 would be a nice choice. It has pink flowers.

This isn't the best picture....

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plant a June next to it ... the blues match .. and the center of June contrasts ....

i also grow rose champion among hosta.. the hot pink/purple flowers glow near the blues ...

ken

'Touch of Class' - a knockout next to any blue - especially Halcyon or Hadspen Blue - the blue middle matches beautifully and slugs HATE it.

Westy

Thank you, all! I have found your comments so helpful! I think I'll have to stick with the hosta, heuchera, lamium, etc. suggestions b/c it's quite shady in that corner of the garden. The rose campion looks really cool but I'm afraid I don't have enough light. :-(

Thanks again to all of you! I knew you all would be able to give me a variety of ideas to work with; that's why I haunt this place every morning with steaming espresso cup in hand in the wee bits o' of the morning. I have written down all of the possibilities & will PURSUE WITH GUSTO!