I think this article in the Washington Post can help us to understand was is neutral or standard Spanish
Accent on Higher TV Ratings
Spanish-Language Network Telemundo Coaches Actors to Use Mexican Dialect
By Frank Ahrens
Washington Post Staff Writer
Monday, August 2, 2004; Page A01
Accent-neutral Spanish is the sound of a coming media culture. Spanish-speakers make up the fastest-growing group of minority media consumers in the United States, according to Nielsen Media Research. Univision encourages accent-free Spanish among its actors, even if it does not enforce it as Telemundo does. And neutralized Spanish can be heard elsewhere, as well: Both presidential campaigns employ it in their Spanish-language television ads targeting Hispanic voters.
The results of Telemundo's work can be heard in "Gitanas," the network's new telenovela about gypsies in Mexico, which debuted Tuesday night and featured actors from Colombia (the male lead), Argentina, Peru, Spain and Mexico, all speaking neutralized Mexican Spanish. Nielsen ratings indicated the show was Telemundo's most-watched debut ever.
Mexican Spanish, Telemundo says, hits a middle ground between Colombian Spanish, which the network considers too fast and terse, and some Caribbean accents that are too slow and imprecise. Telemundo executives say Mexican Spanish is the broadest-appeal, easiest-to-understand Spanish -- if Telemundo's coaches can iron out its typical sing-song cadence. In other words, it becomes the Nebraskan of Spanish.