According to BWP a redpoll with a yellow or orange, rather than red, cap is exceptional, although commoner in captivity. Well, I can't comment on how common this feature is but in a relatively small sample of redpolls (<20 birds) here are two showing this exceptional head colouration! The first is a paler bird, almost flammea like in its plumage with a distinctly yellow cap. The second bird, more typically cabaret has an orange cap. Both birds were seen in direct comparison with others with more normal red or deep pink caps. Any comments?
Edit: according to the Worcester ID paper, these caps are not uncommon on first year or female redpolls.
Here is a screen grab of a Mealy Redpoll on the niger feeder with a Lesser Redpoll. Not a great shot, but it is a digiscoped shot through double glazing - presumably you can see why I dug the hide out!