Strange reaction of color values

I’m in my first tests with Yafray and, as my floor look to dark, i as trying to put it a little less black.

The strange thing is, after some tests i get a very diferent result with just a very little ajust in material color. Is this a bug?
Fisrt image as a 0.05, 0.05, 0.05 grey. Sencond as a 0.051, 0.051, 0.051

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Please, help me in this.
Now i’m trying with a clouds texture with 2 greys, a 0.1 and a 0.12 assigned as 1.0 color.
I cannot get a gradient. The small diference is that black and grey.

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