Technically, MDMA does have immune-lowering effects temporarily and that can make your body too weak to fight off the cold you're getting, and I would think that methylone would be the same.
However, anecdotally, I've taken MDMA right as I was getting sick two or three times in my life and each time I (very weirdly) woke up feeling 100% the next day and then completely got over my cold. It doesn't make any sense, really, and it might not necessarily be a cause-and-effect relationship, but I did find it quite funny!
It's a risk that you'll get that oncoming cold if you get high, but you have to just ask yourself if it's worth the risk. In my case, colds aren't the worst thing so I tend to just do it depending on how sick I feel.