How does vector 3 attribute work?

[TTV_WifeLeaverGaming]

I'm talking about the attribute from the element viewer that you can add. I want to make a character's hair glow and have gotten it to work using vector 3. However I want to set it to be like this in the vmt too. What commands do I have to use and how does vector 3 exactly work?

[Koldraxon]

Process:
1: Apply override materials to the model.
2: Apply Vector3, type in $color.
3: Paint it.
Outside of SFM, I am of no use. Refer to guides or other resources, if there's any.

[Zappy]

In a VMT, a Vector2 is written as "[A B]" (with quotes), where A is the first number and B is the second number, and a Vector3 is written as "[A B C]" and a Vector4 is written as "[A B C D]".