I think this is mythology from the Babylonians, right? Did they give details about Nibiru's characteristics such as the colour of its surface?
I would guess that even if the lost Scrotum Scrolls of the Seer of Seers, the great Afrodamus are ever located the truth will still be held from us but as the Profit Wiggs has so often pointed out, everything worth anything was originally BLACK so the soil of the Mofoland of Nibiru must, by intelligent (and Holy) default be BLACK.
This was hinted at by those bastions of blackness, Pubic Enema, when they released the musical tome, "Fear of a BLACK Planet". It seems that de Troof will indeed set ya'll free... 'n' sheet.