Breaking up hashes into lists based on values in the hash?

gistfile1.pp

$hosts => {
  'a.domain.com' => {
    someparam => somevalue,
    tags => [ 'red' ],
  },
  'b.domain.com' => {
    someparam => someothervalue,
    tags => [ 'red', 'green' ],
  },
}

is there a way of getting lists out of the $hosts hash based on the tags array such that
  
redlist = ['a.domain.com', 'b.domain.com']
greenlist = ['b.domain.com']