If the objects are not grouped or components, selecting all and then using the bucket or dragging a material from the material window works. Of course it works for groups too where no color has been applied to the faces inside the group, but that's not usually good texturing practice, may be OK for you.
Thru paint plugin is pretty much like painting. just hold down the mouse button and run over the objects: depending on your settings it will paint faces INSIDE groups and components as you go. It's a very good and deep plugin. Almost as fast as selecting it all and applying a color.

Now as you say "automate", maybe this is a code development question.

It can be confusing and you really need to read a bit before you get the hang of things, but who wants to read when they have a question to ask.
Share and learn means, share a tutorial or learn by watching one.
There is a pinned post almost at the top of the section pointing out that it is only for tutorials.
https://sketchucation.com/forums/viewtopic.php?f=18&t=8229#p48563
I'm sure there used to be an 'about' saying this but I'm not seeing it easily.

So basically look for an appropriate subforum for your questions, that keeps things tidy and easier to find. The one you suggested would work for this question or even the nebie forum it has been moved to by one of the moderators. Often you question will relate to something specific, dynamic component, an extension, sketchy physics etc and then it is obvious but others can be more general, by avoiding the ones it is not you narrow it down to the few more general ones. It's not overly important but it is good housekeeping and makes life easier for all in the long run.
Very few people get it right from the start.