consider adding terms for dark liver/spleen/bone marrow

[sbello]

We have terms for pale liver, pale spleen but not for dark liver or dark spleen

J:282829 reports darker liver, spleen and bone marrow.

There are other annotations attached to abnormal liver morphology and abnormal spleen morphology that specify dark or darker
No mentions of dark or darker associated with MP:0002397 (abnormal bone marrow morphology)