spotted here, from here, which explains that,
"Ink Calendar" make use the timed pace of the ink spreading on the paper to indicate time.
The ink is absorbed slowly, and the numbers in the calendar are "printed" daily. One a day, they are filled with ink until the end of the month. A calendar self-updated, which enhances the perception of time passing and not only signaling it.
The ink colors are based on a spectrum, which relate to a “color temperature scale”, each month having a color related to our perception of the whether on that month. The colors range from dark blue in December to three shades of green in spring or oranges, red in the summer.