Tulip tree 'Aureomarginatum', Liriodendron tulipifera 'Aureomarginatum', Backlit yellow leaves against a blue sky.

Rocket, Eruca vesicaria sativa. Close side view of leaves and yellow flowers.

Rocket, Eruca vesicaria sativa. Close side view of leaves and yellow flowers.

Cook Strait Kowhai, Sophora molloyi, Panicles of dense yellow flowers dangling among tiny green leaves.

Lemon, Citrus limon, Lemon growing on a branch with leaves covered with raindrops.

African violet, a Saintpaulia cultivar with purple flowers edged with white, around yellow tipped stamen, Graphic top view of one flower with buds and leaves, Rich deep colours.

African violet, a Saintpaulia cultivar with purple flowers edged with white, around stubby yellow tipped stamen, Close view of one flower with leaves, Rich deep colours.

Heliconia rostrata, often known as Lobster claw, Bright red pendula clawlike flowers tipped with yellow and green, surrounded by glossy green leaves, Photographed in Southern Vietnam.

Primrose, Primula 'Appleblossom', Overhead view of one cream flower flushed with pink and a yellow centre, surrounded by a neat rosette of green leaves.

Primrose, Primula 'Appleblossom', Overhead graphic view of three flowers flushed with pink and a yellow centre, surrounded by green leaves.

Primrose, Primula 'Delia mix', Overhead graphic view of one cream flower with a pink ring and yellow middle, surrounded by a neat rosette of green leaves.

Primrose, Primula 'Delia mix', Overhead graphic view of one cream flower with a pink ring and yellow middle, positioned in the centre surrounded by a neat rosette of green leaves.