Heron beak colour

All the images of grey herons in books and on the RSPB site etc. show them with a yellow beak.

However I saw one at London Wetlands Centre yesterday with a much more colourful red and yellow beak. Does this indicate anything?

Heron Heron

(That was in the 'wild side' close to the captive birds area, for those who know the site.) Here, by way of contrast, is one with a more conventional beak I photographed a little while earlier collecting nesting material: