Why am I getting an error when running my torso color script?

You only need one end for a set of if/elseif/else conditionals. elseif acts as the end for the if on line 3.

Per the comment: Yes, just wrap it in a function within the player.CharacterAdded event like so:

game.Players.PlayerAdded:Connect(function(p)
  p.CharacterAdded:Connect(function (c)
    torso = c.Torso
    playercolor = math.random(1,5)
    if playercolor == 1 then
      torso.BrickColor = Color3.fromRGB(242, 243, 243)
    elseif playercolor == 2 then
      torso.BrickColor = Color3.fromRGB(196, 40, 28)
    elseif playercolor == 3 then
      torso.BrickColor = Color3.fromRGB(40, 127, 71)
    elseif playercolor == 4 then
      torso.BrickColor = Color3.fromRGB(27, 42, 53)
    else
      torso.BrickColor = Color3.fromRGB(99, 95, 98)
    end
  end)
end)