Why is the blue chest "not operable"

The chest is out of range.
To be operable place it in the startup area within 32x32 around 0,0 coordinates. (default settings)
or later build an outpost.
The area can grow by research. You can see the current area, if you open a chest.

Where can I use the blue chest?

with default settings the blue chests are working together on a single surface in a shared sector. plus the first level of a Factorissimo building in this sector.
You have a start sector at each surface and you can create outposts.

What is the difference between the chests

The range.

• the blue Chests uses a radius depends on settings.
• the green Surface Chests range is limited to the current surface und first level of a Factorissimo's factory.
• the red Global Chest range is the surface of the current planet and all associated¹ surfaces.
  ¹) This depends on the mods used. For example, for Factorissimo this is ALL levels of the factories. For the Surfaces Mod this includes all sub levels.
• the black Universe Chest has an effect when using e.g. Space Exploration or an other mod that creates addiitional surfaces like planets/moons etc...

If you don't use any other mods. Surface Chests, Global Chest and Universe Chest doing the same.