the color transistors on the neckboard can go wonky if you put fresh caps in that are running full throttle. it's like it stresses the solder joints harder or something like that.
when I capped my Popeye, I didn't have to do this. when I got my Donkey Kong, I had to do it. PC-10, BOTH monitors had to get done (and mine are the Z2AW variety with inverter boards... even more shit to reflow).
you'll probably also observe that you'll have to re-white balance your monitors once you cap them. fortunately, these are pretty easy to adjust. be mindful there are 3 brightness adjustments, the flyback Screen pot (coarse), the Brightness pot (fine), and there's another medium brightness pot as well.
some of these monitors are like 30 years old now, so it's kind of logical for them to have cold solder. once you cap these they look magical, there's so much improvement. especially if you have foldover, like my PC-10 had. wow, it was like night and day.