Improve the explanation on the use of colors (section 3.9)

For better readability and change the focus to the Full Framework:

"In ArchiMate models, there are no formal semantics assigned to colors, and the use of color is left to the modeler. For instance, in many of the example models presented in this standard, colors are associated with layers and aspects of the ArchiMate Full Framework, some of which are shown below. However, they shall not be considered a requirement of this standard:

• Purple for the Motivation Aspect

• Yellow for the Business Layer

• Blue for the Application Layer

• Green for the Technology Layer"

Also, the last paraghraph migth be improved for better readability:

"The standard boxed notation also uses a convention for the shape of the corners of its symbols to represent different element types, as follows:

• Square corners are used to denote structural elements

• Round corners are used to denote behavioral elements

• Diagonal corners are used to denote motivational elements"