To follow 'normal' wiring convention, I would say black to shell (or braided shield), and yellow to pin (center conductor of wlre shown.). It's much more important to be consistent between left speaker and right speaker than the specifics of wire color in your case.
The RCA cable you've shown is really for connecting signals between components at line level, rather than speaker level use. It will work, of course, and you may not notice much different from a RCA that is parallel wire construction instead of coaxial (which is what you have.) But a receiver/amp that uses RCA for speaker output is not going to ask too much of those cables in terms of power handling or other performance issues.
With 2K+ messages, I'm sure you've run across a thread or two discussing higher-end speaker cables, so you're aware there are many alternatives. But the wires you have may be good enough for the components you're connecting, and your intended use. Wire 'em up and listen to the tunes.
On edit: And yeah, do the battery test mentioned above, too.