It's kind of hard to explain, but I'll give it a shot. Yes, small changes in a color can have a profound influence. Whether or not that influence is "lighter or darker" or "more of a color" would depend on the amount of change in relation to the other channels. Small changes in a single channel probably wouldn't have too much impact and would probably just change the hue a bit. Changes that affect all channels could affect the brightness.
The closer the 3 channels are to the same value, the more "white" or "black" a pixel becomes. If each channel has a value of 128, combined they will be gray. If a channel's value becomes higher than the other two, it will start to become more "that color" than gray. And if it's less, it will become less gray and more a combination of the other two.
For example..
RGB: 128/128/128 - a gray pixel, 128/64/128 - a pink pixel, 128/192/128 - a light green pixel.
Assuming the same discrepancy in value just at a different "position".
RGB: 64/64/64 - a dark gray pixel, 64/0/64 - a purple pixel, 64/128/64 - a "forest green" pixel (crayola)
So in short.. it's complicating lol. Comparing the top two examples, the first one became darker, the second one creates a new, darker color since green was eliminated, and the third one results in same color, different shade.
The closer the 3 channels are to the same value, the more "white" or "black" a pixel becomes. If each channel has a value of 128, combined they will be gray. If a channel's value becomes higher than the other two, it will start to become more "that color" than gray. And if it's less, it will become less gray and more a combination of the other two.
For example..
RGB: 128/128/128 - a gray pixel, 128/64/128 - a pink pixel, 128/192/128 - a light green pixel.
Assuming the same discrepancy in value just at a different "position".
RGB: 64/64/64 - a dark gray pixel, 64/0/64 - a purple pixel, 64/128/64 - a "forest green" pixel (crayola)
So in short.. it's complicating lol. Comparing the top two examples, the first one became darker, the second one creates a new, darker color since green was eliminated, and the third one results in same color, different shade.