As flowers age they can lose some of their colour.
The sun can have a bleaching effect and the pigment should already have done it’s job of attracting pollination insects.

Some flowers have petals that are a throw back to an earlier plant cross

Other plants may be programmed to produce flowers with a natural variety in their colouring.

Photographs can lie especially when it comes to the rendition of colour.
The colour temperature and light conditions can make the same pigments appear different in different conditions

Lantana camara often has three colours on one blossom in this case pink, yellow and red.