using automator to rename files automatically

Do you just have a single RGB, CMYK, JPEG folder for all projects?

If so, you could create a Folder Action in Automator. You can have it run when files are added to the folder.

You would make one for each of the three folders, one renaming to _RGB, one to _CMYK, and one to _JPG.

In Automator, create a new Folder Action that receives files added to one of your folders.

Then, drag in a Rename Finder Items and set it up to add Text after the name.

If you have multiple of each folder, you could still do this. If it is a set of folders for each project, I think you would be spending more time building the Automator Folder Action than you would be saving time.

Although you can interactively run an Automator application or Workflow, you cannot do so with a Folder Action that expects a file dropping event to trigger it. That is why you received the warnings because no dropped file was found.

The following simplistic Folder Action in Mojave 10.14.6 (18G95):

will continuously append "_Text" to the dropped filename until it exceeds the maximum file name size. So, for a dropped filename of foo.txt, it becomes foo_Test_Test_Test ... _Test.txt. This is horribly broken, and may be present on High Sierra too. Mine runs without error, but what a mess it makes of the intended filename.

In these cases, I prefer to use a Run Shell Script instead of a Rename Finder Items action, and use Bash, Zsh, or one of the other scripting languages to perform the folder name append to the file.