Okay - this is exactly the problem that occurred to me within 2 seconds of learning how this feature works. If it's going to work any way, it should at least be a GRADIENT from grey to orange. This way of doing suddenly splits your whole user community into two groups, the Greys and the Oranges.
There's a huge difference in human psychology between a gradient and a divider. Not that this is necessarily a good idea anyway - it encourages people not to post on old threads, or even not to post too far off the top of the page, etc. But in any case - if you're going to do it at all, make it a gradient!
While I agree that this is divisive, having a gradient would just defeat the purpose of the feature, which is to highlight those whose examples you should be following.
Making it a gradient makes it really hard to tell who is setting a good example and who isn't.
Rather than a gradient, I'd just like the option to turn it off, even if that option is only available after 50 karma or something. To me it is visual noise.
Even better if it was visible to a user up to X karma and then disappeared past that. Then it would serve its training purpose without leading to a long-term two-tier culture here.
Anyone remember what happened to the Blues and Greens in Rome? To the Eagles and the Rattlers in the Robbers' Cave Experiment? If not, see here: http://www.overcomingbias.com/2008/01/the-two-party-s.html
There's a huge difference in human psychology between a gradient and a divider. Not that this is necessarily a good idea anyway - it encourages people not to post on old threads, or even not to post too far off the top of the page, etc. But in any case - if you're going to do it at all, make it a gradient!