The Common Welsh Green dragon is a smooth-scaled, green coloured dragon.
From the Story
Discovered in Book 4, Chapter 19, The Hungarian Horntail
"The Common Welsh Green dragon is one of the four dragons to be involved in the first task of the Triwizard Tournament. When Harry first visits the dragon enclosure near the Forbidden Forest the dragon is hit with several Stunning Spells simultaneously and falls to the ground, unconscious."
Discovered in Book 4, Chapter 20, The First Task
"Fleur Delacour picks the Common Welsh Green dragon as her opponent in the first task of the Triwizard Tournament. The dragon is placed under a kind of trance by Fleur during the task. It went very sleepy but managed to set her skirt alight when it snored it its sleep."