Note the dark colored (bull) eyes on the birds. These are recessive whites. Those whites that are white because they are a combination of homozgyous ash-red and homozygous grizzle instead of recessive white usually have colored eyes. Recessive white birds may literally be any color genetically under that white (including ash-red grizzle) - a test mating to a bird which is not white and which does not carry recessive white can provide youngsters which may tell you what the recessive white is carrying hidden.
Recessive white Racing Homer -
bird bred, owned & photographed by Phil Bateman.