There’s a small bug in the mozilla addons site that affects some people trying to install “experimental” addons (“Invalid file hash”, corrupted downloads, etc.). The bug has been fixed according to bugzilla.
If you had problems installing AnyColor, please try again or visit this knowledge base article.
Update: The following steps may help solve the issue.
- Enable cookies AND third-party cookies (Tools->Options-Privacy).
- When logging in to AMO, make sure you check the “remember me” checkbox.
- Clear the cache.