Bradley James and Colin Morgan made their own songs while on set of Merlin yet those songs were never to be released in public. Their songs however got posted on YouTube by the fans.
The real Merlin was in fact a Welsh druid. However, Colin Morgan who used to portray Merlin is an Irishman. Colin does speak Gaelic, yet he doesn't speak Welsh, unlike his colleagues actors Alexander Vlahos (Mordred) and Eve Myles (Lady Helen).
Like many other natural blond world famous actors Bradley James was also a brunet & a dark/black hair, depending on a character that he played. He remained blond in real life though for he obviously prefers being blond.
Colin Morgan & Bradley James are virtually of the same height, namely, both of them are 6ft tall. Colin is 1,83m & Bradley is 1,82m tall to be exact.
There is a variety of fan fiction stories posted by the fans on the Web not only about the Merlin and Arthur's alleged romance (aka Merthur), but also a fictional stories about the romance between the both actors, Bradley James and Colin Morgan (aka Brolin), as well.