Brown book uncovered (5)
I believe the answer is:
umber
'brown' is the definition.
(I know that umber is a type of brown)
'book uncovered' is the wordplay.
'book' becomes 'numbers' (book of the Bible).
'uncovered' indicates the central letters.
The central letters of 'numbers' are 'UMBER'.
(Other definitions for umber that I've seen before include "Dark brown coloring matter" , "Natural pigment" , "Yellowish-brown pigment" , "Dark to reddish brown" , "Dark brown (pigment)" .)