From all the descriptions we've received, Elayne's hair is a combination of blonde and red while Aviendha's has only been described as reddish.

No matter which way you cut it, the woman in the middle has hair closer to a golden shade, while the woman on the left can only be a red-head.

Aviendha: "Strongly muscled but softly curved (TFoH, Ch. 31), Aviendha stands taller than an average woman due to her Aiel blood. Her hair is a dark red hue and shoulder length, growing out from her Maiden's cut. Her eyes are a deep blue green that blaze with fire to match her personality and nature."

Elayne: "Elayne is tall for a woman and very beautiful. She face is a perfect oval framed by mass of sunburst curls. Her lips are full and red. Her eyes are bluer than Rand can believe (TEotW Ch. 40), they are like sapphires. Her skin is smoother than finest silk. Straight back, with supple and long limbs."

Also, I think there is confusion as to how "reddish gold" or "golden hair" tends to look since hues can be such a subjective description, but I will say that it should definitely be lighter in shade and hue than hair described as "dark reddish".