I downloaded Deathnote for my server and im not sure how to take the like skull picture off and dont know how to edit the colors for the names. 

  "Variable Colors": {
    "killer": "#C4FF00",
    "victim": "#C4FF00",
    "weapon": "#C4FF00",
    "attachments": "#C4FF00",
    "distance": "#C4FF00",
    "owner": "#C4FF00"
  },
  "Chat Format": "<color=#838383> {message}</color>",
  "Chat Icon (SteamID)": "76561198077847390",

In the config\DeathNotes.json, right down the bottom.

To change/remove the skull pic, you'll have to make a new steam account I think with the picture you want. Hopefully the plugin dev or @Wulf will chime in with how to change/delete that.

As ElDubyaOZ said you can edit that in the configuration file.
The "Chat Icon" is represented by the steam ID of the account you want to use the profile picture from.
To show the default rust icon simply enter "0" as the chat icon.