What does arbitrary color mean?

To answer the question... What does arbitrary color mean?

When the colors an artist uses are not based on what he/she sees but chosen arbitrarily. The term implies that it has no meaning but it may have a symbolic meaning or emotional meaning.

In the painting above Matisse is using arbitrary color. The color does not try to match what is actually seen. The color is being used as a compositional element to balance the composition. The color creates rhythm and balance.

Look at the just the blue areas. The blue is placed in patches as the red and yellow are. If you follow the blue around the canvas it seems to simulate how our eye jumps around a scene stitching together our experience.

What do I need to buy if I want to start learning how to draw?

Here is my answer to What do I need to buy if I want to start learning how to draw?

Get a sketchbook, a pencil and practice all the time. That said I like to use a 2mm lead holder with 4B lead. Staetdler makes one with a point sharpener in the end. I like it because I can carry it with me and I don't have to worry about sharpening. It even works out to be less expensive if you compare the cost of drawing pencils and how much gets wasted in sharpening! A kneaded eraser is pretty great to have. I use the black hard bound sketchbooks 9x12 or sometimes 6x8. You don't need anything special but getting new toys certainly can be inspiring and keep you going.

What are rules and tips for foreshortening an object?

Here is an answer to a question about foreshortening.

You can figure out foreshortening by using the rules of perspective. It would be too complex to describe the rules of perspective here, but in a nutshell...

The basic idea of linear perspective is that objects in space look smaller the farther away they get from the viewer. If you learn to draw a box using linear perspective you will be able to draw boxes that appear to be in a three dimensional space. Anything can be put into a box. The parts of a thing can be broken up into smaller boxes. Even figures and the parts of a figure can be placed in boxes. The more you can master the rules of perspective the easier it will be for you to draw things in a 3D space. You will understand how and why things look foreshortened.