The "scale effect" is a very contentious issue. Many people feel it's crap, but there is a physical basis for the effect.
If your eyes were 12 inches from a 1/72 scale aircraft, the size of the model is the same as the actual size of the full size plane if it were 72 feet away. At that distance, you can't see rivets or panel lines.
Also, due to diffusion of light through the atmosphere between subject and viewer, shades and colors tend to wash out somewhat. A case in point - take a color chip in your hand and stand 72 feet from a large object painted the same color. The color of the full sized item will appear lighter than the color chip in your hand.
There are rather complicated physics that I don't fully understand that explain this effect fully, but rest assured there is a valid scientific basis for the claim.
In truth, whether you do or don't apply the "scale effect" is purely up to you.
I do tend to lighten aircraft colors for small scale planes just a tiny bit - for some reason it just plain looks better, even on a "factory fresh" plane.
In the end, you just have to do whatever you think is best for yourself, and nuts to anyone who doesn't like it.
Cheers
LeeTree