mabey you have been pressing it to much on colours 3d. you should just play a differant game for about a week then mabye it will be fine. the same problem happned to me with mario kart 7

As far as I know, if you are painting a picture on Colors! 3D, and you pass over 6 hours of playback footage, the undo button won't undo anything anymore. I've experienced this a lot on Colors, as lots of my drawings have taken a very long time to paint. If your paintings aren't taking very long to paint, or the problem is occuring whilst playing other games, you may want to consider having someone look at your 3ds to check for faults. If you've only had the 3ds for a few months, you should still have the guarantee that came with the console when you bought it. You can use that to exchange your 3ds for a new one if the one you have is faulty. Hope this helps. :)

Apparently, It doesn't work on my camera either so... yeah!

'Giving it CPR' works! Blow into the sides of the button. It should work.

My friend has a DSi, and I told him to try the method, since his L&R buttons weren't working. He did it, they were fixed, and I blew his mind xD

THAT'S UNBELIEVABLE! It worked! Mr. Everyone(FB), you rock!

You're welcome! c:

Yeah. The blowing trick works for all the ds genorations. Unfortunetly the left trigger on my ds lite is broken entirely. (like... the whole triggers about to fall out broken.)

blow on ur 'R' button
then wait a couple of days then itll work better than ur 'L' button :]