I found the following about the Red Dragon:

"The red Welsh dragon "Y Ddraig Goch" owes its origins to folklore and Arthurian legend. Originating from a serpent representing the Welsh God Dewi, Celtic King Arthur was said to have had a dream about a red dragon (symbolically representing Wales) which slayed a white dragon (which represented the Saxon invaders). In later times a crude red dragon design was adopted by Prince Llywelyn of Gwynedd in the 7th Century and taken into battle by Welsh hero Prince Owain Glyndwr in conflicts with the invading English. In later history, at the Battle of Bosworth, Welsh-born King Henry VII (Henry Tudor, crowned 1485) unfurled the red dragon, which he in turn had adopted as his own emblem. As such, the beloved red dragon has always represented the defiant Welsh nation; iconising Wales's unique cultural and historic heritage as a proud and ancient nation which has long survived external threat. The Welsh dragon is often associated with the motto, "Y Ddraig Goch a ddyry Gychwyn" - or "The red dragon will show the way".

The Wikipedia article talks about a prophesy, which mean it has not yet come to pass...