That's how it worked in July - if anything has changed, hopefully someone will chime in.
EDIT: yeah, Jarod is right. Radiator Springs Racers will run out of Fastpasses early in the day. Get those before worrying about World of Color Fastpasses (or consider getting the meal package that includes the World of Color viewing area if you're super concerned).
WOC is currently having a Christmas version of the show that just premiered & there was an AP limited time magic promo, so that is having an impact on fast passes, but even with that being said.....go for the RSR fast passes first.
If for some reason you are unable to get a RSR fast pass, take advantage of the single rider line if possible.
Fortunately, a Radiator Springs Fastpass won't count against you, so you can immediately get one for another attraction. I'd opt for Soarin' Over California. After grabbing this pass, go get your World of Color Showpass. Since this is not technically a Fastpass, it doesn't count against you either, and they rarely run out before mid-afternoon as long as there is more than one show (if you want the later showing, check back a few hours after opening). Finally, go to California Screamin' and get a Fastpass there as well (fun fact: Due to the ridiculously high capacity of California Screamin' it is not connected to the Fastpass loop so you can hold a Fastpass for it and another attraction in DCA at the same time (at least this was true as of my most recent visit in September). I once used this fact to get 10 rides on California Screamin' on a crowded day).
Depending on how willing your party is to split up, single rider lines are available at all of DCA's Fastpass attractions except Twilight Zone Tower of Terror. With the exception of Soarin' Over California, I've found the single rider line to typically be quicker than the Fastpass line, especially when the return time wait is factored in.
Walt Disney World's Magic Kingdom
Disney's Animal Kingdom
Disney's Hollywood Studios
Disney California Adventure
Universal's Islands of Adventure
Universal Studios Florida
Universal Studios Hollywood