This is a simple little program that gives the idea of how the figures are made by a computer.
Below on the left we see a piece of the image of a sunflower; on the right, an enlargement of it.
As you can understand, the image is made up of many small squares of different colors.



Each small square is identified by a pair of numbers, which indicate its row and column.
Three other numbers indicate its color, as will be seen later.

This little program allows us to create, in a similar way, simple figures, making us better
understand how these images are made.
Let's see, for example, how a figure like this can be drawn:

                   

The little program has only a few commands:



On the left we can choose the drawing tool, among the following:

draw      ->  it draws a curve, moving the mouse (slowly)
fill      ->  it fills the inside of a closed curve
rectangle ->  it draws a solid rectangle
pick      ->  by clicking on a point, it takes its color as the current color

I can then choose the color. I can do it in several million colors. All colors are achievable
by putting together different "quantities" of red, green and blue.
Computers allow you to combine 255 quantities of each of these colors together.
A few examples (some colors are given different names):

                   R     G     B
                  255    0     0    ->   red
                   0    255    0    ->   green
                   0     0    255   ->   blue
                   0     0     0    ->   black
                  255   255   255   ->   white
                  128   128   128   ->   grey
                  255   255    0    ->   yellow
                  255   165    0    ->   orange
                  237   145   33    ->   carrot
                  255   192   203   ->   pink
                  150   75     0    ->   brown
                   0    255   255   ->   cyan
                   0    128   255   ->   azure
                  178    0     0    ->   strong red
                  255    0    255   ->   magenta
                  128    0    128   ->   purple
                  128   255    0    ->   chartreuse
                  128   128    0    ->   olive green

I can choose the colors with a click on a bar and then select them better with the numeric
codes, in different ways depending on the "browser" you are using. In some browsers the
most frequent colors are highlighted.

             

     

Let's see how I can make the previous figure.
(1) I select the yellow color then, with "fill", I color the background with yellow. (2) I select
the color red and, with "rectangle", I draw segments (ie "thin" rectangles), until (3) I obtain
the word "CIAO". If I want, I can cancel one or more of the last commands with "Undo".



(4) I select the blue color and with "draw" I draw (moving slowly) the outline of the petals.
(5) Then, having selected the green, I trace the outline of the set of small central petals
(those that are yellow in the daisies), and then I fill the inside with "fill". (6) Finally,
having chosen a color (strong red), I also fill the outer petals with "fill".

If, then, I want to change the color of the central part and I want to put the same color (a
particular yellow) as the background, I can select "pick" and click on the background to assume
as "Color" the same yellow.

                   

The figure I made then I can, if I want, register by clicking the "Save" command.

With the keys "Ctrl +", "Ctrl -", "Ctrl =" or (using Mac) "Cmd +", "Cmd -", "Cmd ="
I can change the size of the image (and more easily trace the points). 

Another example (I drew rectangles of different colors):