Apply full vim colorization for bash scripts that have no shebang line

So in my project there are many bash script files that are sourced, but never run directly, so they get no shebang line and no execute bit set. Vim colors them a little bit, but doesn't use the full colorization. How do I tweak vim to give me all the normal bash colors for these files?

EDIT:

Without shebang:

With shebang:

EDIT 2:

There is an answer that works for file-by-file changes below, and I'll go with that if that's all I can get, but what I'd really like is to modify a config file or something else in my vim installation so that I always get the full "with shebang" colors even when there is no shebang. There must be a file somewhere that defines the incomplete colorization, which I can just replace with the file defining the complete colorization.

EDIT 3:

The vim global variables set are not substantially different, as seen in these images (output of :let g:):

Environments

Diffed

I'm sort of at a loss here.

EDIT 4:

I dumped the entire environment from a properly-colored window (left) and an improperly-colored window (right), and diffed them, finding this:

60 b:current_syntax       bash   |   61 b:current_syntax       conf

So, for some reason it thinks my shebangless source files are conf files. So I need to figure out how to match them to bash instead.