After Effects preview with decreased image quality
You're probably using "Fast Draft" as your preview. This is a new preview mode which uses the GPU to provide "fast"* rendering for previews. This mode will generally look pretty bad, with less or no antialising, lower resolution textures, and less accurate colour.

You can go back to the old adaptive resolution rendering for previews, or use final quality (it actually works faster sometimes, go figure) using the little widget at the bottom of the comp window:



*Adobe's words, not mine, IMHO the latest versions of AE are the slowest yet