def set(index, r, g, b)
			check_index(index)
			self[index] = Color.new(r, g, b)
		end
def set(index, r, g, b)
			check_index(index)
			self[index] = Color.new(r, g, b)
		end
Set given pixel identified by +index+ to +r+, +g+, +b+

 See <tt>[]=</tt> for a method that takes +Color+ instance instead
 of individual components