This is what I came up with after reading through many pages of AForge.NET and OpenCV documentation. If you apply the saturation filter first, you might get a dizzy image. If you apply it later you will get a much clearer image but some "light green" pixels might have been lost before while applying the HSV filter.
// apply saturation filter to increase green intensity
var f1 = new SaturationCorrection(0.5f);
f1.ApplyInPlace(image);
var filter = new HSLFiltering();
filter.Hue = new IntRange(83, 189); // all green (large range)
//filter.Hue = new IntRange(100, 120); // light green (small range)
// this will convert all pixels outside the range into gray-scale
//filter.UpdateHue = false;
//filter.UpdateLuminance = false;
// this will convert all pixels outside that range blank (filter.FillColor)
filter.Saturation = new Range(0.4f, 1);
filter.Luminance = new Range(0.4f, 1);
// apply the HSV filter to get only green pixels
filter.ApplyInPlace(image);