The context you mentioned refers to the index in the array ```colors```. I searched for calls to ```dc_output()``` and looked at the passed values and I think their meaning is something like this:
Context/color index | Meaning ------------------------ | ----------- 0 | commands send to gdb 1 | ouput/responses from gdb 2 | output of received errors 3 | output of "(gdb) " prompt 4 | error output from scope itself