Waheguru Ji Ka Khalsa, Waheguru Ji Ki Fateh
Saffron color for the banner was selection of Guru Hargobind (Indirect deduction. Gurmatt Martand, S.G.P.C., page 616) and was not blue to begin with. At the time of Guru Gobind Singh, the color of Nishan Sahib changed to blue, and Nihangs maintain the tradition. In the Maharaja Ranjit Singh period, Nishan Sahib was blue (Dr. Harjinder Singh Dilgir, World Sikh News, June 30, 1995 AD). After the Maharaja, may be under the influence of Dogras (majority environmental effect) it became white. Baba Naaena Singh and Akali Phoola Singh left the color of the Akali-Dal flag yellow, but changed Dastaar (see Dastaar) to antimony. Some use antimony color for Pharera (flag) which is not a tradition. They seem to derive this color from the color of the turban of Guru Gobind Singh. It is not clear as to how and when the color returned to saffron (A discussion with Dr. Bhai Harbans Lal, Arlington TX, USA).
source: http://www.sikhmissionarysociety.org/sms/smsarticles/essaysonsikhvalues/ensignofdignity/