Allow color to initialize from an existing color object

Setting a 2d object's color to be random is great, however it's difficult to
re-use that color without manually extracting out the rgba values from that
color object. Ideally it would be convenient to be able to do this:

```ruby
square = Square.new(color: 'random')
square_two = Square.new(color: square.color)
```

This patch allows this behavior from any 2d shape, making it much easier to
reuse those random colors :)

1 files changed, 3 insertions, 0 deletions

diff --git a/lib/ruby2d/color.rb b/lib/ruby2d/color.rb
index be223d3..8b72dbb 100644
--- a/lib/ruby2d/color.rb
+++ b/lib/ruby2d/color.rb
@@ -66,6 +66,8 @@ module Ruby2D
           end
         when Array
           @r, @g, @b, @a = [c[0], c[1], c[2], c[3]]
+        when Color
+          @r, @g, @b, @a = [c.r, c.g, c.b, c.a]
         end
       end
     end
@@ -90,6 +92,7 @@ module Ruby2D
 
     # Check if the color is valid
     def self.is_valid?(c)
+      c.is_a?(Color)   ||  # color object
       @@colors.key?(c) ||  # keyword
       self.is_hex?(c)  ||  # hexadecimal value