Hi, The yellowish green bruise you have in the middle of your lower back is due to any recent trauma, injury you had without noticing. Perhaps, you stay too long sit in a chair. Perhaps, the chair you use are not comfortable, giving systematically light injuries without noticing. The yellowish color means that it is under the healing process. At this point, can apply heparin cream to reduce bruising. If it will not improve by time and other bruises will appear, you should consult a physician and run further tests to evaluate blood disorder: - coagulation tests - complete blood work Hope it helped! Dr.Albana