I tried switching to the basic palette with fewer color, though it might be slightly better, it is still much worse than it was before. In fact it never used to be a problem, so something must have changed, or some kind of bug crept in. I checked the activity monitor, and it seems that ASP almost used the double amount of CPU when I have the color editor open. This seems abnormal to me.
I hope a quicker fix can be made than to wait for the next big update, which might take months.