Body Color script is not working? "Player is not a valid member of workspace"

You need to wait() for yourself OoOoOooo SPooKY anyways, try this..

game.Players.PlayerAdded:Connect(function(p)
    wait(.5)
    local char = p.Character
    for _, v in pairs(char:GetChildren()) do
        if v.ClassName == "Part" then
            v.BrickColor = BrickColor.new("Bright Yellow")
        end
    end
end)

Also, If you cannot see the face, just remove the accessories from the player ;o

What I did: When the player is added, it waits .5 just in case the character wasn't added, then it runs a loop in the character hoping to find the legs, the head, arms, etc cause you said "body color" and not "head color" and then I change it to bright yellow.. YEEET

The issue you have is more likely to be that the script ran before the character was even there. You don't need to do game.Workspace.newluigibro since there is a property of the Player's instance which is player.Character which returns the actual player. To accomplish what you are trying to do you can use the event player.CharacterAdded which is fired every time the player's character is spawned in.

game.Players.PlayerAdded:Connect(function(player) -- fires every time a new player joins.
    player.CharacterAdded:Connect(function(character) -- event of player which returns the character

        local head = character:WaitForChild("Head") -- Waits for the head to be added
        head.BrickColor = BrickColor.new("Bright Yellow") -- Sets the head to the new BrickColor, Bright Yellow!
    end)
end)