A white theme among the green shades in my back garden at the moment, though I didn't plant with that in mind. Above is Three-Cornered Leek (Allium triquetrum).

Intermediate Periwinkle (Vinca difformis)

Summer Snowflake (Leucojum aestivum)

White Comfrey (Symphytum orientale)

Honesty (Lunaria annua var. albiflora)