Avoid overwriting passed hash when LayerColor.new.

Hi. `Joybox::Core::LayerColor.new` should be avoided side-effect to passed options.
please see below.
```ruby
my_opts = {color: [255, 255, 255]}
Joybox::Core::LayerColor.new(my_opts)
Joybox::Core::LayerColor.new(my_opts) # => layer_color.rb:40:in `new:': expected Array of 4 elements, got 5 (ArgumentError)
```

thanks.