Color-coded for freshness

Many of the streets here in Berlin are lined with large horse chestnut (Aesculus spp.) trees, and for the last few weeks, these trees have been adorned by large clusters of flowers, or "candles".  Some of the trees have white flowers with yellow, orange, or dark pink markings...

A "candle" of horse chestnut (Aesculus hippocastanum) flowers.

... while other trees have pink flowers with the same yellow, orange, or dark pink markings.

A "candle" of red horse chestnut (Aesculus × carnea) flowers.

Meanwhile, the sidewalks beneath the trees have become littered with white and pink flowers.  Interestingly, though, all the fallen flowers have dark pink markings.  A closer look at the flowers still on the trees reveals that those with yellow markings have fresher petals and anthers (the structures that hold the pollen).

New flowers have yellow markings, which then turn orange and pink as the flowers age.

It is also only those young flowers that produce nectar to reward pollinators.  Thus, the different color markings enable visitors such as bees to quickly discriminate between rewarding and unrewarding flowers.  Nevertheless, the older flowers may help attract bees and other potential pollinators from a distance by contributing to the overall size of the floral display.