Try this code:
WriteConsole(0, GetPlayerStat(Killer,'Name') + ' is PWNING!', $EEFFFFFF);
Note:
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Only use single quotation marks if the enlcosed content is presentable as string.
Be sure that you're using a suitable procedure or rather function for this code, otherwise you will get a compile error.
For example this one:
procedure OnPlayerKill(Killer, Victim: byte;Weapon: string);