LINEAR SYMMETRY AND CMYB COLOUR

A Linear symmetry is the type of symmetry in which a line is drawn from the middle of the figure.
The two parts of the figure coincide, then each part is called the mirror image of the other, the part of the figure on one side of a virtual line falls exactly over the other part. Such a figure is called a symmetrical figure.
The line wich divides the figure into two equal parts is called the line of symmetry.
Shapes or figures may be horizontal, vertical, both horizontal and vertical, infinite and no line of symmetry.  http://www.math-only-math.com/linear-symmetry.html

Simetría axial y cuatricromía from ESTER ALONSO

If you want to get what you can see on the examples you will need a basik sheet of paper (A4), tracing paper, an HB pencil, and coloured pencils as well. In order to get saturated colours you will also require felt tip pens.

You are going to search for a picture such a portrait on a magazine. The face has to be completely facing forward in such a way that you can divide it into two symmetric parts by a vertical axis. (Both parts have to be equal when folding the paper over this line).

SUBSTRACTIVE COLOURS: CMYK (From Webopedia)

Short for Cyan-Magenta-Yellow-Key (Black), and pronounced as separate letters. CMYK is a colour model in which all colors are described as a mixture of these four process colors. 

CMYK is the standard colour model used in offset printing for full-color documents. Because such printing uses inks of these four basic colors, it is often called four-colorprinting.

In contrast, display devices generally use a different color model called RGB, which stands for Red-Green-Blue. One of the most difficult aspects of desktop publishing in colour is colour matching -- properly converting the RGB colours into CMYK colours so that what gets printed looks the same as what appears on the monitor.

Here you have an interesting video on substractive colours and colour printing.