MacOS – How to periodically run a script/command when a specific application is being used

In my opinion, the best way to do it is by using Apple's own task scheduler: launchd, because you don't need to install third-party software. First, the theory: to run a script from the command line, you just run:

osascript /PATH/TO/YOUR/script.scpt

Knowing this, all you have to do is create a plist file in ~/Library/LaunchAgents/ with this:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>air-mail-beta.job</string>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/bin/osascript</string>
        <string>/PATH/TO/YOUR/SCRIPT</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
</dict>
</plist>

The name of the plist file doesn't matter, but it should be in ~/Library/LaunchAgents/. Also, make sure to change /PATH/TO/YOUR/SCRIPT accordingly.

Finally, you just need to tell launchd that you want this script to always run. To do that, you just do:

launchctl load -w ~/Library/LaunchAgents/NAME-OF-YOUR-PLIST.plist

and you're done! If it looks like the script didn't start, you can do this:

 launchctl start air-mail-beta.job

where air-mail-beta.job is the property under <key>label</key> that we've set in the plist file.

Finally, should you ever need to disable the script, don't forget to unload it with:

launchctl unload -w ~/Library/LaunchAgents/NAME-OF-YOUR-PLIST.plist

I know this solution is more technical, but trust me, that's a better way to deal with your issue. If you have any question, just ask!

You can use Keyboard Maestro's mouse actions to find an image on the screen (such as the colour wheel), then a defined pixel coordinate within the found image to click on. This will therefore select the same colour regardless of where the window is located.