For a bold look, try golden
yellow 'Schwellenburg' with other yarrows and purple Penstemon
barbarbatus 'Prarie Dusk'
The golden yellow color seems to blend
with pastels or bright colors equally well.
For a softer, more pastel look, try 'Schwellengurg'
with Achillea 'Salmon Beauty'
above and below with white Valeriana officinalis