It means that which is:
•fully ecstatically wondrous
•beyond joyfully amazing
•intensely orgasmically blissful
Nathan Fillion, on his Twitter page, kindly acknowledged my entry work defining his recommendation of the new "in" phrase: "Double Rainbow" on Urban Dictionary! He said it is "Full on." Thank you, Nathan. You are so Full On Double Rainbow!
The TV shows Castle and Firefly are so intense, they are Full On Double Rainbow!.
Serenity, the feature film starring Nathan Fillion, is so vivid, it's Full On Double Rainbow!
Nathan Fillion is so awesomely spectacular, sexyhotmessgorgeous, and brilliantly talented, his fame is sweeping across the nation, and over all the world! Nathan Fillion is Full On Double Rainbow!