I'm naturally a dishwater blonde. I color it red.
Natural reds fade with age, though. Sunlight can lighten the ends.
For porosity, you can run you finger up a loose strand of hair from tip to root. Non porous hair will feel more slippery, and a porous one can feel quite bumpy.
Also, drying time with product free hair is a good indicator. My product free hair can be dry in about two hours, which is pretty fast. Non porous hair can take 12-24 hours to be totally dry.
Porous hair can be moisturized, but it has a hard time with moisture retention. Non porous hair can retain moisture, but it can be hard to actually Moisturize.
Porous hair tends to show weather and humidity changes more dramatically than non porous hair. Not that you can't see this with non-porous hair, but you *really* notice it with porous hair.