You didn't ask but I thought I would tell you anyway, coreopsis looks great with just about everything! Over the last two years I've acquired several types of coreopsis and experimented with it in different combinations and found it plays well by itself and with others. Here on the left is one of our two 'Moonbeam' coreopsis plants beginning to bloom. Even when not in bloom the threadleaf coreopsis plants look cool just because of their feathery, fern-like foliage.
This is perhaps one of my favorite combinations. This seed raised coreopsis (I believe its a descendant of coreopsis 'Sunfire') blends well with the red of the Paprika yarrow (achillea) next door. These two companions are growing and thriving in the rain garden. Achillea is one of those plants that you can divide and divide and divide. Several small sprigs of achilea that I transplanted last fall are already becoming descent sized first year plants about to bloom.
Why not try yellow on yellow? As long as the yellow isn't exactly the same shade it works! In this case the coreopsis 'Sunfire' is hanging out with the daylilies. The oddest thing about these daylilies is that they are so yellow companred to the divisions on the other side of the sidewalk. They all came from the same plant but the daylilies nearest the house are much more yellow than their siblings.
And though they aren't close yet the new additions of 'Jethro Tull' and the 'Orange Pixie' Asiatic Lily will be best of friends before long. Spacing is important since this coreopsis should eventually fill in the gap between them.
Coreopsis comes in colors other than yellow but the only one I have that isn't yellow hasn't bloomed yet. I'll show you it as it decides to bloom. Coreopsis is very easy perennial to grow from seed and well worth it. It's low maintenance, drought tolerant, and has few pests. My coreopsis actually survived the leaf beetle larvae attack earlier this spring. What more can you ask for in a perennial? Have you planted one yet?