Contrast:
The objective of contrast is to produce maximum visibility . An item is more noticeable with more contrast.

Colour/Value:

One of the greatest possible contrasts in visual design or art is the difference between black and white (value contrast) . Colour contrasts can be strong but usually not as strong as value contrasts. Bright colours attract more attention than dull colours.

Size:

When it comes to being noticed bigger is always better. There is a place for all different sizes in the scheme of layouts. Size plays an important role for concentrating other elements for a comparing reference to portray increased attention.

Shape:

An unusual shape can call attention to itself but it is not as strong a contrast as size or value/colour.

Fig. 128: Value contrast among elements and space.