Royal Watch: Prince Charles is back in the colonies this week. He's due to arrive late today in Dallas, where his armor-plated Jaguar will be waiting, to help celebrate the 150th anniversary of Texas' independence from Mexico. Someone had suggested it be called "Jubilee 150," but that sounded a bit too "sissy" to them there tough Texans, so it is simply referred to in the more manly word "Sesquicentennial." While there, Charles will cut a Texas-size, 90,000-pound birthday cake that will be assembled by forklift and can feed 300,000.

Charles, who has a special affection for the megarich, will also be there for Tuesday's black-tie dinner, where he will present the Winston Churchill Foundation award to Texas billionaire H. Ross Perot, a flag-waving exponent of conservative causes who symbolizes so much of what Texas has become. First Lady Nancy Reagan will also be at the dinner. Later in the week the traveling prince will be in San Antonio and Austin, where he will visit with former first lady Lady Bird Johnson and San Antonio Mayor Henry Cisneros. And then it's on to Palm Springs, Calif., that ghetto for the exclusive rich, and a little polo for charity.

Royal Watch addendum: Princess Anne may be expecting. Then again, maybe not. Now, after all that talk last year that her marriage to Capt. Mark Phillips was in trouble because they rarely appeared at official functions together, the British press is speculating that she is expecting her third child. The Palace, of course, is confirming nothing. Time will tell or show. Local Talent

In the past couple of years, the Washington Performing Arts Society has gone to great expense for an annual gala to raise funds for a "concert in the schools" program. In 1984, opera great Luciano Pavarotti came and performed and last year television star Diahann Carroll. Both cost a fortune and, as with so many other big charity events, a vast percentage of the money went to pay for the party, with much less going to charity.

This year, the gala will turn to a recognized Washington talent who won't cost any money. At the March 15 dinner in the J.W. Marriott Hotel, widely admired and enjoyed pianist John Eaton will perform in concert. As Derrie Blount, chairman of the dinner, said, "We felt we should promote our own." Eaton, who performs at the Embassy Row Hotel and continually sells out his Smithsonian concert series, may not be a national name, but it's doubtful that anyone will leave the March 15 concert disappointed. Volcker's World

Newsweek magazine has a major profile on Federal Reserve Board Chairman Paul Volcker in the current issue describing him as the second most powerful man in America. Much of the article talks about Volcker living in a small Washington apartment with green milk crates for end tables and watching a black-and-white, 10-inch television set.

As is so predictable in a piece about a government official, the article talks about the great financial sacrifice Volcker made to go to work in government, in this case, leaving a $116,000-a-year job to take one at $75,000. On that he has to maintain two residences and his wife had to take a job as a bookkeeper because she didn't move to Washington. According to Newsweek, she has arthritis and diabetes and doesn't want to be far from her New York doctors.

It must be difficult for an unemployed Youngstown steelworker or a struggling Cedar Rapids farmer to understand the hardship of existence on $75,000 a year. They must also feel concern for Washingtonians, who must not have as good medical care as New Yorkers do. Those readers out in America are also smart enough to know that once a federal official returns to the private sector, he more than makes up for the few years of financial sacrifice. End Notes

Former Pittsburgh Steelers quarterback Terry Bradshaw, who has an eye for a well-turned form, was married for the third time this weekend, this time to law student Charla Hopkins at Texas Woman's University. His previous wives were Melissa Babish, a former Miss Teenage America, and figure skater Jo Jo Starbuck . . .

Academy Award-winning actress Shirley Jones finally has her star in Hollywood's Walk of Fame. Holder of star 1,822, Jones won her Oscar for her role in the movie "Elmer Gantry." She also starred in such films as "Oklahoma," "The Music Man" and "Carousel," and was in the hit television series "The Partridge Family" . . .