Question

why are the Corolla of the flowering plants are colourful​

Answer 1

The petals composing the corolla are typically brightly coloured or white and attract insects and birds for pollination (see below Reproduction: Pollination).

Answer 2

$Hi \: \: there!$

The Corolla of a plant is usually attractive because the vibrant colours of corolla help plants to attract more insects and birds that help in pollination which is beneficial for the continuation of the species of the plants.

Hope it helps! ♡