Marbling affects color pigments. M genes causes these pigments to change. In the early years M genes only causes color loss (at least in my experience). But now I see M genes causing color loss then regaining color - either returning to the previous color or changing into something different, sometimes changing 3-4 different color or pattern. .... Now I can understand why it's called the "jumping gene".
Yes, marbling can affect any color - regular, metallic, and dragons. Now M gene is also used to induce certain colors to appear (this is still here say because I haven't had any real experience to verify this).