You have to increase the Diffuse Color Multiplier as by default the input shader multiplies the base colors, meaning it will always make them darker. So put it up at 2 or something, with the same input color settings, and it should work fine. If you're using very dark input colors, use a higher multiplier (or lighten your input colors). I admit that this is a bit confusing that the defaults do not produce results that are generally similar in lightness to your original though.
And yes you're right that it varies the entire object, not per-leaf. So working directly inside the object with the Default Shader inputs is the way to go for per-component color variation.
- Oshyan