If it is a common, this is definitely a bad sign. There are other plecos that actually slightly change colors as they mature, but not commons. As other people mentioned, usually a sign of stress. My commons change colors when I am forced to move them to bigger tanks, but it always goes away within an hour or two.
Yes, he will probably be fine until then. If he is still white after a week or so, and you dont have your new pump, then I would get worried. I'm sure you know this, but just make sure you try to get the water to close to the same temp. before you add it. I only mention this because when I do a 10% water change with water that is only around 5 degrees off of what my main tank is, my pleco will get whiter for 5-10 minutes, so it obviously stresses him.