Why are the dots not colored or colored?

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).