As has been mentioned, Apple only signs versions of iOS for so long. Once Apple stops signing a version, you cannot restore (revert) to it. You can only restore to the current version that Apple is signing (or in some cases, the latest version a device can run).
Sometimes there are problems, and the usual resolution is to restore your phone. As also has been mentioned, doing that means you have to restore to the latest version of iOS. Eventually that will mean iOS 7.
Coming from Android you may be familiar with the concept of rooting and custom ROMs. I have the same objections to what I see in the current iOS 7 beta as you do. I'm really not into all the pastel colors. I've got two young kids and I see enough of that on a daily basis, I don't need it on my phone.
But at some point iOS7 will probably be jailbroken, just like iOS 6.1.2 and below are now. Jailbreaking is roughly equivalent to rooting/custom ROMs on an Android. You can modify things to your liking. Right now I am jailbroken on iOS 6.1. I am waiting for iOS7 to be jailbroken before I upgrade. After that I can apply themes to change the look of iOS7 while still having the new functionality (which is similar to a lot of current jailbreak tweaks by the way).
Most likely the same team that jailbroke iOS6 will jailbreak iOS7. In the iOS6 jailbreak the upgrade/update feature was disabled so that you couldn't accidentally lose your jailbreak by pressing the update button. It also removed the upgrade/update notification badge. I can only speculate that this is something they would also include in an iOS7 jailbreak, which would remove any notification of further updates for you.