Answer to Question 1
There are several kinds of color deficiency, which are sometimes referred to as kinds of color blindness.. Least common is rod monochromacy, also called achromacy. People with this condition have no color vision at all. It is the only true form of pure color blind- ness. In this condition the cones are nonfunctional. They see only shades of gray as a function of their vision through the rods of the eye. Most people who suffer from deficits in color perception can still see some color, despite the name color blindness. In dichromacy, only two of the mechanisms for color perception work, and one is malfunctioning. The result of this malfunction is one of three types of color blindness (color-perception deficits). The most common is red-green color blindness. People with this form of color-blindness have difficulty in distinguishing red from green although they may be able to distinguish, for example, dark red from light green. The extreme form of red-green color blindness is called protanopia. The other types of color blindness are deuteranopia (trouble seeing greens with symptoms similar to protanopia) and tritanopia (confusion of blues and greens, and yellows that disappear or appear as light shades of reds).
However, most media designers are well-aware of the importance of not relying on color alone as a cue or indicator.
Answer to Question 2
The Mller-Lyer illusion involves two lines of equal length. One line has outward facing arrows on each end, pointing away from the line and the other has inward facing arrows, pointing towards the midpoint of the line. In this illusion, we tend to view the equally long line segments as being of different lengths. Oddly enough, we are not certain why such a simple illusion occurs. Sometimes, the illusion we see in the abstract line segments is explained in terms of the diagonal lines at the ends of the vertical segments which may be implicit depth cues similar to the ones we would see in our perceptions of the exterior and interior of a building.
Life cycle of Obelia, a colonial cnidarian.
European wildcat feeding its kittens, as illustrated in Brehm's Life of Animals
Lycophyte Life Cycle
The early stages of the human life cycle.
Four color theorem
Segregation of alleles for seed color