Sheet material comprising at least one watermark having a colored shade

A sheet material, comprising:

• at least one first layer having at least one first color;
• and
• at least one second layer comprising at least one watermark having at least one second color, that differs from the first color,
• wherein the first layer incorporates at least one dyeing agent in its mass, said at least one dyeing agent of the first layer chosen so as to give said first layer a colored shade appearing approximately continuous to the naked eye, and
• wherein the second layer is a fibrous layer comprising a dyeing agent incorporated in its mass and at least one internal sizing agent configured for limiting or preventing penetration of the at least one dyeing agent of the first layer into the mass of the fibrous second layer comprising said watermark.