Moom applies a fade in/out when you invoke/release the (optional) onscreen keyboard controller and cheat sheet. If this fade annoys you, here's how to remove it:

1. Quit Moom and launch Terminal (in Applications > Utilities).

2. Paste the following line, then press Return:

   defaults write com.manytricks.Moom PMWindowFadingDuration -float 0.0

3. Relaunch Moom.

Hopefully this causes the fade to vanish; if it doesn't, you're being bitten by OS X's aggressive caching of preference values. From that article, the best fix is this to quit Moom, switch back to Terminal, paste killall cfprefsd, then press Return. This relaunches the prefs system; now relaunch the app, and it should read the modified prefs file.

If you'd like to undo this at any point in the future, repeat the above steps, use this Terminal command (again after quitting Moom):

defaults delete com.manytricks.Moom PMWindowFadingDuration

This command deletes the custom setting you added; when you launch Moom the next time, the fade will be back.