How to get hairdye out of carpet/walls (and general stains)?

Dye is permanent and the only product that might remove it would be a bleaching agent like peroxide or chlorine bleach... each of these is likely to affect the undyed portions of your carpet as well, however. If the splatters are small and the carpet is pile/shag, your best bet may be to try to cut out the individual fibers. On the wall, touch up paint will be your best bet. When I dye my own hair, I cover surfaces with an old towel and even have a "designated" sweat shirt I wear so I don't ruin my other clothes. Good luck.