Why are flowers colourful?

Red, orange, yellow, blue and lilac-whatever the hue, the spectacular colours of flowers are all tools in the service of reproduction. Plants use the bright colours of their blooms to attract pollinators such as insects and birds. This also explains why the flowers of plants that are pollinated solely by the wind, such as grasses, tend to be rather nondescript. They don't need to look attractive.
           Some flowers, like that of the horse chestnut, will even inform their pollinators when it's no longer worth paying them a visit. Brown stains develop inside the bloom as soon as it has seen fully harvested and is empty. Pollinators then lose all interest in the flower and can target other, more inviting blooms.