Can anyone answer these Cheers questions?

Unfortunately, I am only able to answer your final question:

The reason is because the yellow lettering represented full beer glasses (beer is typically yellow-ish), while the white lettering represented empty glasses. Therefore, the symbolism of "Cheers" ending, i.e. no more beer. Kind of ironic since Norm left his beer unfinished in his final scene. But, of course, like Martin Crane telling his son Frasier, "Thank you" in the finale of "Frasier," or Geoffrey the butler calling Will Smith "Will" instead of "Master William" in the finale of "The Fresh Prince of Bel-Air," a character has to say/do something out of character to emphasize the bitter sweet moment. To continue, the pitch blackness during the "Cheers" credits also represented the end, of course. Similar to when rapper Jay Z retired (or so we thought), thus his "final" album "The Black Album" with the CD artwork being simply that: black. Hope that helped. :-)

As for the last ending it was the final episode and they wanted to go out differently and quickly. I liked it. Along with Sam's revelation.

I thought no one else noticed it was actually "Unchained Melody". Good catch. I assumed they thought it really was the "correct" song(their naivete) or they couldn't get a copy of it. And if they knew they figured no one else would catch that error. I'm an ex-DJ and noticed it right away(the most popular slow song ever for a long time) it was in "Ghost" so it was brought back into the public eye(ear).I met the gentleman that wrote "Unchained Melody" for his wife at a songwriting seminar.