When the "Classics" line came out at the end 2006, it was pretty immediately popular with long-time fans, who had been largely starved for new toys of "Generation One" characters at that point. Although the line was fairly short-lived, intentionally making way for the line of toys created for the first live-action Transformers film in the summer of 2007, "Classics" gave fans about a half-year to focus on the characters they remembered and loved from their childhoods. It also gave Hasbro a chance to do a few repaint homages to offer to stores as exclusive sets. The "Battle for Autobot City" set, featuring Ultra Magnus and Skywarp, was exclusive to Target in the US. Both of the toys in this set are repaints, and in fact both molds have already been featured multiple times on this blog, so I'll just direct folks to the original uses of the molds, Optimus Prime for Ultra Magnus and Starscream for Skywarp, and simply direct readers to the search engine at the top of the page if interested in tracking down the others.
While both toys feature decos that are clearly inspired by their Generation One toys, neither is as close to copying those original color schemes as later G1-inspired toys would often be. "Classics" was intentionally an attempt to update and homage, rather than simply copy. That said, if being told that the Ultra Magnus toy, in particular, homages the Generation One toy comes as a surprise to you, I should mention that Ultra Magnus continues a trend which started with a 2004 repaint of the original Masterpiece Optimus Prime, basically just reusing that same mold in a white deco. Such "white Magnuses" trace their origin to the original Ultra Magnus toy from 1986, which itself was a reuse of a Diaclone-era figure that reused the cab portion of the toy that became Optimus Prime. However, because Ultra Magnus hid that "white Prime cab" behind a larger robot form created out of the toy's trailer, many fans never realized this heritage if all they knew was Ultra Magnus as he appeared in the 1980s cartoon. Sadly, my "Classics" Ultra Magnus suffers the fate of older plastic toys, in that it has visibly yellowed in the past decade. Skywarp doesn't seem to have suffered as badly, but of course, all plastic toys yellow with age. White toys simply hide it worse than others.
I'm not at all clear what the name given to the set, "Battle for Autobot City," is intended to reference. The most obvious possibility is the scene at the beginning of the 1986 animated Transformers: The Movie, which is often referred to by that (or a similar) name, but neither Ultra Magnus nor Skywarp were the main characters in that battle, and they certainly aren't known to faced off against each other specifically, so I'm hesitant to make a significant claim on that point. The back of the package describes a situation where Skywarp is actually leading forces with a plan to kill Ultra Magnus to "prove himself to Megatron," all of which seems a bit out of character for Skywarp, but there it is. Ultimately, this was just a convenient way for Hasbro to release a couple more toys while the "Classics" line enjoyed its brief lifespan.