Dithering

Dithering is a technique used in pixel art to achieve a gradient like effect. To dither you must create a pattern using the two colours you would like to blend. To create the gradient effect the pattern should have more of one colour towards the edges of the dither, and an equal ammount of both colours in a the centre. You aren't just limited to the patterns shown above either, you can create your own pattterns or even make the dither completely random if it suits your artwork. You can also add more colours to your dither to enhance the effect even more.