Pink and orange (light and medium) will take care of most of your pan fishing needs. I never used the yellow or green (MH and H) for anything. When you get into spoons that heavy, the springs do you no good at all. Get a light action (or was it ML??) action rod and a pink and orange spring for it. The UL action is too light for anything and the M is too heavy for panfish.
Good Luck!
I used the St. Croix system for a few years until I started building my own rods with Marmish springs. They work good!
Tip: Take the rod out of the tube and inspect it for crooked or loose guides before you buy it. These rods are built from quality components in another country, the craftsmanship can be ugly.