For me it would be hard to miss:
I knew the dyelots were different, so I was completely prepared for this to happen. I thought alternating the new ball with the remaining of my last ball every 2 rows would be okay. Obviously, the difference would still be quite visible.
So, I ripped back 10 or more rows before the joining of the new ball. It's always a hard decision to rip a project using Kidsilk Haze ... anyone who has used this lovely yarn knows that ... the loveliness just vanishes when you try to frog. But there is a trick, though, which can make the hard task easier ... kind of like being caught in Devil's Snare (do you read Harry Potter?) ... you have to make the fuzzy yarn relax and go slow.
Then, I joined the new ball and switched between the 2 threads every row. Much better:
The new ball is more like stone-washed version of my own 2 balls, which are much richer in colour. But then, when you run out of yarn in a discontinued colourway, you don't really have the luxury to match the dyelot, right? :)