Here is the error message I got today *** No rule to make target gtkcolorsel.c', needed bylibgtk_3_la-gtkcolorsel.lo'. Stop

The reason for that is because the output files from previous builds make Automake unhappy.

The solution is enter the jhbuild shell, and do: git clean -xdf

More details from GTK+ IRC: automake does not like when files get moved around so you need to clean up the build tree and get it back into a pristine state