It seems like if the gradient doesn't extend exactly to the object's boundary that either a lighter or darker colour extends beyond the gradient.
If you make a freeform gradient with 2 points - 1 a light colour and the other dark - and ensure the points remain within the middle area of the object you'll see that the colour that extends to the edges doesn't match either colour from the gradient.
It seems like if the gradient doesn't extend exactly to the object's boundary that either a lighter or darker colour extends beyond the gradient.
If you make a freeform gradient with 2 points - 1 a light colour and the other dark - and ensure the points remain within the middle area of the object you'll see that the colour that extends to the edges doesn't match either colour from the gradient.