Most likely over time this spot will fade. I've seen discoloring like this on an Inferno, but it was only where the track was. Looked kind of odd, because there was this whitish/grey ring all the way around the ball. I have seen the ball since then and it no longer has the ring. Looks like it will go away, just not certain how, why, or when.
If you've had the ball for a while and use it a lot, a trip through the Hook Again process might take care of it. If not you're only out the cost to get that ball working like new again.
Just my $2/100...
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The summer... time to get my ARSEnal in gear!