The review of the Field Notes Colors subscription we published yesterday was more timely than even we knew. Today, they unveiled their new “Snowblind” edition for the 2015 winter season. Let’s cut to the chase: They change colors in direct sunlight. Indoors they’re white, outdoors they’re blue. So awesome.

They’ve got some usage tips to keep in mind:

Direct sunlight works best. Most types of glass filter a great deal of UV light, so the color-change effect is greatly diminished through a window. The effect is also diminished early or late in the day when the sun passes through the atmosphere at a greater angle.

Unlike regular UV ink, Photochromic ink does not glow under a blacklight (watch video), though some blacklights (watch video), ultraviolet LEDS (watch video), and heat lamps do emit UV light and can activate the pigment.

Create temporary images and patterns on your books with stencils (watch video), household objects, plants, or photo negatives (watch video). Any object that casts an interesting shadow will work.

Long-term exposure to UV light will fade the ink and reduce the color-changing effect, so keep the books out of direct sunlight when you’re not using them.

It’s weird but kinda cool that memo books would come with instructions. The body pages are 60# Finch Opaque text paper marked with a very faint gray graph, and the books are bound with glossy white staples.

As always, these 3-packs go for $10 each at fieldnotesbrand.com. Or, subscribe to Field Notes COLORS (while supplies last) and they’ll immediately ship you two “Snowblind” 3-Packs plus two standard-edition 3-Packs.