When I render, the color changes This is a 2D intro title animation of a couple of solid color geometric figures (rectangles, circles etc.) moving in layers on top of each other, and put the camera right overhead. They are all in purple-ish colors. When I run it with the "play animation" button, the colors are what they should be. But when I render it (ctrl + F12) to a movie, all the colors are changed to green-ish colors. It's really only the color of the figures that changes, not the entire video.

When I render each frame to a picture, there is no problem. But there are over 400 frames, so that is impractical.
As noted by @DuarteFarrajotaRamos you have a node in the compositing that is altering the result.

You have a Hue Saturation Value Node changing your color.