Amergin the Form

I am blue : but not new I am white : sometimes bright I am red : and then delight I am yellow : often mellow I am marine : but not green I am light : but not at night I am black : when sun ,I lack I am grey : who but I Sees in , both night and day Amergin an early Irish poet who used this form . A puzzle in words to decipher Welkin = see category for this poem