[FIX] mail: restore pre v11 note color
[FIX] mail: restore pre v11 note color

The gray-lighter was modified at 88881e9f to make it lighter (#F9F9 instead of
Restore the previous grey and increase contrast.

To quote "The Non-Designer's Design Book by Robin Williams":

> Contrast is created when two elements are different. If the two elements are
> sort of different, but not really, then you don't have contrast, you have
> conflict. That's the key–the principle of contrast states that if two items
> are not exactly the same, then make them different. Really different.

opw-1835722

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo