As it is most of the times, you will find the answer in the German Trademark Act. According to Section 3, the signs eligible for protection as trade marks are:
(1) All signs, particularly words including personal names, designs, letters, numerals, sounds, three-dimensional designs, the shape of goods or of their packaging as well as other wrapping, including colours and colour combinations, may be protected as trade marks if they are capable of distinguishing the goods or services of one undertaking from those of other undertakings.
Are you unsure about your soon to be business trademark? Let us examine your case and your trademark. This is the easiest way to reduce the risks of an unexpected refusal.