What -- and how much -- does Colin Powell owe the Republican Party?

I'm watching Pat Buchanan on Hardball with Chris Matthews, and Buchanan is whining and showing his true self.   Can someone toss him a box of tissues?   Earlier today Colin Powell endorsed Barack Obama for president.  From his interview on Meet the Press, Powell spoke of:

• the conduct of McCain's campaign (focus on inconsequential issues and attacks)
• the choice of Sarah Palin to be McCain's running mate and her obvious unreadiness for the office of Vice President of the United States (a question of McCain's judgment), while Obama chose one, Biden, who is ready on day one
• the need for a new generation of leaders with new ideas and perspectives, who reaches out to others and practices inclusion 
• supporters of the Republican ticket making disparaging comments about its opposition
• the Republic party's ever narrowing approach to the campaign
• the Republic party's double offense:  trying to convince the public that Mr. Obama is a Muslim, simultaneously implying that being Muslim casts a dark shadow anyone who is of the Muslim faith.

Evidently Buchanan was not listening last month when Powell said that he is an American first and foremost.  He went on to say that he while he had not decided on which candidate he would support, that he would not vote for Obama because Obama is Black.

There was no need to read between the lines when Buchanan spoke on a special edition of Hardball on MSNBC.  After citing all of what the Republican party had done for Powell - promoting and elevating him above many other qualified individuals (as if Powell was not qualified for and did not earn his promotions and appointments, but was given them), in essence he said that Powell is endorsing Obama because he is Black.  

Powell has served his country for 40 years.  He no longer answers to a Commander-in-Chief.  He has a right to exercise his constitutional rights now in a way he never could as a military officer or cabinet member.   Or is he expected to continue to accommodate the desires and whims of those with whom he does not agree -- just because?  If so, because what?  

After giving 40 years of his life in the service of his country, what does Powell owe the Republican party?