The propellent is contained within the can so I don't know if the lack of gravity would have that much effect. Or would it?

What about temperature? Could the can be wrapped in an insulator to make sure the paint doesn't freeze?

Would there need to be a funnel or cone leading from the top of the can to the surface being painted that contained a more normal environment?

Future tech can be used to make this viable. I'm just having trouble figuring out how the paint would actually act in open space.

The composition of the paint will be a problem. Most paints dry by evaporation. that does not work well without gravity if I understand right. It will diffuse out of the paint but will linger as a cloud around the ship.

One idea is to use a hot melt system where a sheet is laid over the panel or panels, and then a heat source is applied to the sheet, melting it to the surface.

Aother method would be applying sheets that are the paint. They "glue" on as the surface coating.

Something that could be done is to apply a skin, a baggy, over the surface, gluing it along the edges. The area is then "flooded" with color under pressure, whther filling it full of liquid or filling it with a gas or spray. It is kept on until the surface coating density is achieved, then the rest of the material is drawn out. Pressure might be applied at one end and a vaccume is applied at the other and it draws out the remains so the skin can be removed.

Don't forget the possiblitiy that a panal might be removed, painted inside, then reapplied. there might be replacement panels so they simply are swapped at the moment so the interior of the ship is not exposed for very long.

Ah, I just thought of something as I was about to sign out. One can use rollers or sponges to paint the surface. The paint does not transfer without physical contact. Usually thick paint does not splatter and physical application is necessary, so one can avoid the worst of flying splatters.

Of course, you asked about spray painting.

Applying a pressurized spray booth on the surface of the ship and the operator sprays the suface with a good filtering system to remove excess paint spray might work.

Of course, if you want the literal spray painting the ship, the electrostatic method of painting would work best.

Issues:

• Hyper rapid evaporation of solvent carrier (thinner) will render ineffective or freeze paint vehicle (binder medium) before surface contact and leave widespread blemishes in finish if evaporation doesn't prevent adhesion altogether.
• Ineffective mechanical adhesion from nonwet application due to rapid solvent evaporation.
• Most enamel-based paints rely on oxidation to cure and harden finish and for chemical adhesion properties, won't cure in a vacuum.
• Synthetic resin-based paints, hydrocarbon plastic coatings actually, cure in ultraviolet light, but problematic to mix and solvent and catalyst (Methyl Ethyl Ketone Peroxide, MEKP) evaporation still an issue.
• Water soluble and low volatile organic compound, VOC, paints rely partly on evaporation for cure, partly on oxidation, partly on ultraviolet light, rapid evaporation of solvent still an issue.
• Gaseous propellant sprays will freeze and clog sprayer nozzle, plus freezing vehicle and carrier solvent, and evaporation problems.
• Rapid extreme temperature fluctuations in outer space would require a costly thermo-stablized paint for any long duration application.
• There's other issues but this is a front-end listing of the immediate issues.

Powder coat paints are actually dry powder enamels applied by electrostatic deposition. But they need controlled, relatively high heat curing in order to set in place. Most plausible painting method in a vacuum.

Three practical reasons for painting, preservation of a substrate, labeling, art or vandalism. Painting a vessel's surface that is exposed to vacuum seems highly impractical and unnecessary. Quick, convenient, and easy labeling of small or large areas in a vacuum would be practically impossible by most conventional painting methods. For art or vandalism? Seems to me that would be equally if not more impractical.

I can imagine one scenario where future tech might solve most of the issues. Ultraviolet light protection coated nano-miniature paint balls shot onto a surface that burst on contact with a substrate and cure instantly in vacuum due to ultraviolet light exposure.

I will have to come up with some gadget that addresses all of these issues.

Electrostatic painting can work quite well for many substances. One thought I had is that photocopier ink is made up of the ink itself, a magnetic material that is attracted by electrostatic charges, and a plastic that is melted so the ink is bonded to the surface.
If the spray painting is done in several stages, they could spray the "paint" onto the surface. then pass over it with a heater to melt it to the surface.

Another method is to use an epoxy like material where it is combined in the nozzle when it is sprayed and the chemical reaction happens moments later, usually once it was attracted to the ship surface.

If it is a chemical process that requires the surface of the ship (the old finish as a possibility) to act like a catalyst to cause the reaction to set up. The setup finish would work great as the electrostatic spray causes the finish to attach to the surface of the ship and only that which makes contact freezes into the paint. The rest floats away harmlessly, or to slowly drift onto another part of the ship.
If this is a ship yard, one could have an entire system to clear the space of the paint dust, dragging meshes or plates through the area to gather up the dust.

The painters might need to torch the surface. The ship plating would have to be able to take great heat so applying heat to the paint to weld it to the surface should not be a problem.

Open space would give the same quality as painting a car outside. Dust, moisture, gas all effecting quality. You could have lots of fun with ionization and static charge issues in open space.

Inside a space dock or a space vehicle the environment can be controlled, temperature, static charge, solar winds not blowing micro particles of paint over things.

If it is on a spinning space station, or if you have some form of artificial gravity, the pressurized spinning bay would be like painting in gravity.

One would simply filter the fumes out of the air. Of course, most everybody would be in space suits anyway, but we are used to working in a pressurized gravity environment so painting in dry dock would be a solution.