Before you start slathering hair color on your extensions, make sure you are working with human hair. Hair extensions come in many forms, both human and synthetic. Synthetic hair absolutely, without a doubt, cannot be dyed. Make sure the hair extension package indicates "100-percent human hair." Anything that says "synthetic" or "yaki" is a no-go for chemical coloring. Also, stick with blond extensions for bold color. The lighter the hair, the brighter the color.
Choose semi-permanent hair color over permanent. Hair extensions are not attached to your scalp, so the oils from your skin won't keep them moisturized. Semi-permanent hair color is typically ammonia-free and will do less damage to the extensions than permanent color. Over-processed extensions can end up looking dry, dull and frizzy at the ends.
Mix the hair color together according to the manufacturer's directions. If you want even less work to do, buy a pre-mixed temporary hair dye that you can store and reuse over and over again. Pre-mixed dyes are typically super-bright and bold, so they're a good option if you're looking for a dramatic look.
Lay out a piece of aluminum foil on a flat surface and drape the extensions over the foil. Hold the top of the extension with one hand and paint hair color onto the extension, from top to bottom, with a tint brush. Fully saturate the hair with color; otherwise you'll end up with a banding effect or uneven color.
Let the extensions process for the amount of time recommended. It's pretty much the same routine as dyeing your own hair, except you don't have to walk around with a head full of foils or a coloring cap for 20 minutes.
Rinse the extensions with lukewarm water until the water runs clear. There is no need for shampooing, which will just fade the color faster. You can dry the extensions naturally or use a hair dryer. Once the extensions are dry, install them and show off your new sexy locks.