the black and white drawable should be composed by well separated (closed) areas, so that you can click on one pixel of an area using the fuzzy select tool (which select the entire closed area) then fill it with the colour you like.
If the areas are not "closed" this easy technique doesn't work.
A partial example
original
Attachment:
th.jpg [ 13.42 KiB | Viewed 2933 times ]
partially colored
Attachment:
th-col.jpg [ 24.25 KiB | Viewed 2933 times ]
note: in the example the selected area has not been growed as usual by 1 pixel before filling it, so you see faded margins