Calyx and corolla
The outer two whorls of a flower. Neither makes a gamete, and a flower without them would still be able to reproduce — but far less often.
1. Calyx
The calyx is made of several sepals. It is the outermost part of the flower, and it is situated in a whorl on the receptacle. It is green in colour.
Function: the calyx supplies protection to the inner floral parts at the bud stage.
2. Corolla
The corolla is made of several petals. It is situated inside the calyx of a flower. It is white or coloured.
Functions: supplying protection to the inner floral parts at the bud stage, and attracting insects for pollination.
Why the colour is there at all
Both whorls protect the bud, so the corolla's colour is doing the extra job. A petal is an advertisement, and it is aimed at an animal. That is why the flowers pollinated by wind and water — which have no one to advertise to — have dull, small petals or none at all.