The Colour Explorer was built as a simple but playful demonstrator to showcase the media metadata filters and colour search developed by Europeana in 2015.
Whilst the principal goal is to show the colour search search, it also uses functionality that allows filtering not just by license, but also to just items which have thumbnail images and those which are available at a certain resolution for direct download.
The entire app is client-side and each page is built from a single API call.
Opening the landing page picks a random colour to display, from a palette of over 200 colours. The user can then experiment with combinations of colours, and bespoke views can be shared e.g. culturepics.org/colour/#/FFD700/B22222/ (the view shown in the image here)