Colin Powell was a Republican when being a Republican was cool. Especially a black Republican. In 1996, it was clear he had a real chance to win the Presidency of the United States. He is known as the author of the "Powell doctrine" which most people seem to agree with, but Presidents don't seem to be able to execute very well on the battlefield. Instead of defining a clear mission, going in with overwhelming force, acheiving the mission, and then leaving. As a nation we have repeated become bogged down in political correctness and posturing, as well as difficult political/armed conflicts.
Powell has never really had a coherent domestic policy. I remember him asssociating himself with conservatism when it was popular. Nowadays he the poster child for "moderate Republican".
All in all, I don't think he was ever really a Republican. It was just politics. A branding. Powell came to power in a time when the public was leery of black liberal Democrats. Especially Powell as a military man had a unique chance to define himself in the center/right. Yet, every time he had the chance policy wise, he chose the center/left. Even if he dressed it up with Conservative rhetoric, he is a Democrat. On issues like Affirmative Action and Abortion rights he didn't even try to hide.
So it is not sensible for Republicans to take cues from a person who is not one of them. Never really was. Powell is the kind of Republican they would get after they have already won.
Me personally, I'm very skeptical of people who admit to voting for Obama and Bush.
I like President George W. Bush as a leader. I like President Obama as a leader.
But it's hard to see how you vote for both unless you just really want to be on the winning side.