Yellow flowering plants started to bloom as if they were saying - 'summer is knocking on the door!'. Indeed, the colour of yellow reminds us on sun and warmth. Yellow and blue really look great together. I have blue Geranium magnificum 'Rosemoor' planted near yellow Achillea.
I really love the blue colours of geranium. They love semi-shade and thrive in rich, moist soil. Usually, I divide them every three years to get the new plants.
Geranium 'Orion' (a single plant!)
This yellow fellow is Onothera tetragona, Sundrops. If you want to cheer up a dreary corner in the garden this is an ideal plant to plant. It spreads well and makes dense patches with no weeds between! The flowers close up in the evening. Grows best in full sun and tolerates the drought.
The blue coloured bell flower.
Well, foliage too can be 'blue'. I have two medium sized Hosta plants with blue foliage. 'Halcion' is one of the well known blue-leaved cultivars.