>In a form label back color is 236,233,216 and page back color is 236,233,216
>
>So I think that the fact of back color of label show darker is a bug,
>Is it correct ?

Not quite - the page back color would be 236,233,216 if you weren't using themes. With themes, it's probably having a slight gradient, and your label is over the lighter part.

You can turn the themes property off for the page, or make label transparent.