Mac OS 8.5 and later came with full on themes (colors and desktop images). Mac OS 8.0/8.1 was the first version with the built-in ability to display images as a desktop background (and came with a few interesting ones and some extras on the installation CD). System 7.5.x and Mac OS 7.6.x had some interesting tiling patterns, but to display full images in System 7.x to Mac OS 7.6.1 you needed a third party app called Decor
Additionally, starting in Mac OS 8.5 the system supported full theme changing of the interface... and Apple included a number of examples in the 8.5 Beta, but sadly pulled those and the documentation on how to make them by the final release. That didn't stop people from reverse engineering themes of their own. The only time Apple stepped forward to stop anyone was when people made an Aqua theme that looked like Mac OS X.
Here are some of the Mac OS 8.5 Beta Themes and the Aqua theme that I have on my PowerBook 3400c/200...
I'll go through and see if I can find some of the earlier tile patterns that came with 7 (I don't have a system running any version of 7 right now).
On the subject of ads, I started using Macs not because of an Apple ad but an ad for an application called Theorist
that I saw in a Physics Today
magazine back in 1989. The ad was similar to this one...
When I found out that the software was Mac only, I quickly found my platform of choice. Even using systems like NeXT, SGI and Sun (none of which I could afford) moved me from Macs... well, until Apple acquired NeXT at the end of 1996, then I started paying especially close attention to NeXT (which ran on PCs by that point).
To give you an idea of what Theorist
is like, here it is running on my PowerBook Duo 2300c/100...
Which is using a NeXT
theme, which is better seen here...
And an image comparing Mathematica
on that same system.
So Apple didn't convince me to use Macs, it was a completely different company's application.