A couple of years ago, a group of entrepreneurs successfully Kickstarted a little something known as the Chameleon Pen. In a nutshell, it's an art pen that changes color tone as you draw – for example, a green Chameleon Pen's ink progressively goes from light green to dark green as the ink is applied to the paper. The same group is now back with Chameleon Pens Color Tops, that change between two completely different colors.
The original Chameleon Pen works by mixing colorless toner with alcohol-based ink, within the nib. As the user draws, the brush-type nib starts by dispensing a light-colored ink/toner mix. As they continue to draw, however, that mix is gradually replaced by undiluted ink, resulting in a darker version of the same color.
The Color Tops work in a similar fashion.
Designed for use with existing Chameleon Pens, each one consists of an ink-filled reservoir that is placed on the drawing end of the pen. Ink of one color is wicked into the nib from the Color Top, mixing with ink of another color that's already been absorbed from the pen. As a result, the nib starts by drawing in the one color, then blending over to the other.
And yes, the pens can also still just be used as regular solid-color pens.
There are a number of pledge levels available in the current Kickstarter campaign, which has already exceeded its funding goal. If you're looking for a set of five pens with five Color Tops, though, it'll cost you US$30 – assuming the tops reach production.
Examples of what can be done with Chameleon Pens and Color Tops can be seen in the following video.