Get any basic color I want without making a new material?

Yes and easy. You can simple create material instance from material like this on picture. You have vector parameter with red color. In material instance you can set this color to any value, rgb,
Then you can set this value via blueprint.

you have full answer in this thread: BluePrint change Base Color of Material - Rendering - Unreal Engine Forums so, more description here is not need I think.