In the black & white serials, Noel Neill's hair appears dark brown to me. It may have been reddish brown--but that's impossible to tell. After she took over from Phyllis Coates on the T.V. show and once they went to colour, then her hair was a reddish brown.
I always figured that they gave Lois reddish brown hair in the comics after Crisis as a tribute to Noel Neill. However, in MAN OF STEEL, she still had the blue-back hair colour. The change didn't disturb me, because I reasoned Lois had blue-black hair in her early days at the Planet and then she dyed it. What bugged me was when they reprinted MAN OF STEEL, they changed the colour to reddish brown.
I figure that Lois is entitled to have whatever hair colour she wants. She wouldn't be the first woman to dye her hair--or wear a wig. I had a kindergarten teacher who had a selection of wigs--it was always a guessing game what colour her hair would be on any given week--pink, blonde, jet black, blue, brown, platinum.
Erica Durance went through many different hues when she played Lois on SMALLVILLE. My canon is that Lois doesn't show her natural hair colour--whatever that might be (only her hair dresser knows for sure)--her hair is changeable.