Bedding is the cement which is laid to secure the ridge or hip capping tiles in place. Often over a period of time the cement will/can crack, and in some cases - completely fall out from its original place, leaving tiles and ridge capping unsecured.
In the past, oxide was added to the cement to give it colour to best match the tile for a more finished look. These days cement may still be used, but once the cement has 'set' a Flexible pointing is then applied - which expands and contracts according to weather conditions. This then forms a strong bond between the roof tile and the ridge capping providing less opportunity for cracking to occur.