Yes, that's right.
The "up" and "down" quarks have different quantum numbers and won't annihilate. For example, an up quark has a charge of +2/3, and the down quark has a charge of -1/3. If they annihilated, this would violate the law of conservation of electric charge.

An up anti-quark, however, is a different particle from a down quark, and has opposite quantum numbers to an up quark. It will cancel out exactly with an up quark.

So a proton, wwhich is made up of two up quarks and one down quark, is stable. A neutral pion, with a up quark and an anti-up, is unstable and annihilates into two or three photons in the blink of an eye.
( Amish Information Systems hates misplaced, commas, Mon 3 Jun 2013, 15:53, 1 reply)

Ah, thank you Amish Information Systems.
Your sig states that you consist of more down quarks than up quarks, does this mean you are a neutron?
(Thor McLegend FUCK SHITPANTS PAC MAN, Tue 4 Jun 2013, 13:50, closed)

No,
...but since most atoms have more neutrons than protons, I worked out that, overall, the "down" quarks win.
( Amish Information Systems hates misplaced, commas, Tue 4 Jun 2013, 21:58, closed)