Seasons of Chaos
Dragons live on the Plane of Dax and are born out of Dax's Blight. It is rumored that the chaos god sought to be the most powerful of all Dragons and in his pursuit killed his brethren. Without servants to bask in his glorious form Dax became lonely and so he created the blight so that he would could be properly appreciated. A Dragon's bite passes on the blight, however the smaller Dragons, like scorpions, carry more venom and are more toxic than the larger ones.
Larger animals that are bitten turn into larger Dragons who have more physical power and stronger breathe attacks. However the blight feeds off of evil and chaos; those so aligned are more drastically effected by the bite and may grow into stronger forms. This can be into larger Dragons or brighter green Dragons. The more bright the Dragon the more intellectually capable it is. Brighter Dragons have an innate connection to the power of Dax and can use that connection to create magical energy and cast spells. The colour, or how green a Dragon is, is also a representation of its rank amongst others. The more green the higher the rank and more control the Dragon will have over others.