Hi Sharon,
Occasionally they develop yellow flowers - just natural variation. A variety growing on Motiti Island has yellow flowers and cuttings have been taken from trees there. Your plant may have been descended from this stock as pohutukawa do not grow naturally south of East Cape or Taranaki. There is variation in pohutukawa flower colours with some having pinkish and orange hues.
Info here:
http://www.tcdc.govt.nz/NR/rdonlyres/638827D7-7F10-44BA-A809-7A2BB7CBA891/31882/TairuaTreeMasterplan2005.pdf
http://www.teara.govt.nz/TheBush/NativePlantsAndFungi/TallBroadleafTrees/3/ENZ-Resources/Standard/1/2/en#breadcrumbtop
They can flower from November into January - mainly December so nothing unusual there.
Males or females? Whoah no idea. I'm no botanist but I had a look and it appears that the flowers have both female and male stages - they are hermaphrodites.
http://www.botany.hawaii.edu/faculty/wong/Bot602/Schmidt-Adam.pdf
Cheers
16 Dec 2008