Question

Why are the dots not colored or colored?

Answer 1

Closed circle is including that number on the number line. Open circle designates that it's not that number.
For example, and open circle on 2 with an arrow right/greater than, the numbers that apply are any number greater than two, but not two. So it can be something like 4 or 2.0001 or 2.01.
A closed circle on two with an arrow to the right/greater than means it CAN be 2 (but it still can be the other numbers as well).