Why is the colour of the texts written by inks appearing Yellowish and Purplish and not the printed one? I was revising some of the concepts from my old copies and I noticed something really weird (might not be weird for others). The texts with black pen when seen from behind the page had some yellowish and somewhat purplish  appearance  (as shown in figure)
1 : 

2 :

3 : 

(the texts might not be clearly visible in the last one) . Also the third one was observed on the pages of a book while the first two were on the pages of a copy.
1 : So I just want to know how is this happening ?
Edit : After reading @niels nielsen's answer , my above doubt was cleared but I have still  a question which he didn't referred in his answer.
2 : Why doesn't this same phenomenon happens with the texts printed on the paper of books ?
So help me with them .
 A: You are demonstrating paper chromatography here, in which the diffusion speed of a chemical in wet paper depends on its chemical characteristics, including its molecular weight, and can be used to separate mixtures of different chemicals.
Black ink is actually a mixture of different dyes that are chosen to tint the basic black so it pleases the eye. Yellow is a common addition. Here, the yellow dye is penetrating the paper faster than any of the other color components, and once the water evaporates from the ink vehicle, the colors are locked in place.
This effect does NOT occur in printed books because the colorants used in book-printing inks are pigments ground into fine particles and the ink vehicles are not water-based. In addition, it is common for high-speed printing presses to use inks that cure to hardness under ultraviolet light, which chemical reaction renders them almost completely insoluble.
Anyway, you can greatly magnify this effect by putting a piece of paper in a shallow dish, wetting it with water, pouring off the excess, and then touching the pen tip to the center of the piece of wet paper. Ink will be drawn into the paper and then the different dye components in it will segregate themselves out in concentric rings of color.
