Try these steps:
1. Fully shut down your Mac
2. Restart your Mac
3. Immediately press the Shift key and keep it down
4. Let go of the Shift key when you see the login window (NOTE: If you have FileVault enabled you may need to log in twice).
5. Take a note of what happens (i.e. how does your Dock look, etc)
6. Exit Safe Mode by restarting your Mac as normal
7. Now check to see how your icons look
I've already tried that. It's not the applications themselves, but rather the folders in the applications folder in macOS. Adobe Premiere Pro CS6 is a purple folder with "Pr" on it, but Photoshop, Flash and a few others are just the standard blue Apple folder icons. It's just really ugly looking, but multiple re-installs haven't seemed to help either.
I don't know if you are using your original DVDs, so try downloading a fresh installer here and try again.
What version of MacOS are you running?
Just in case: Download a Suite installer if you have a Suite serial number because it won't work on a single Photoshop app.
CS6 came out in 2012 and MacOS has moved on, so not everything is going to be perfect.
MacOS High Sierra does not officially support CS6, and you can tell since you have to use Terminal to run the installer.
Adobe will not either. CS6 is way past official support, so you are asking volunteer users such as myself.
I don't know of anyway to "hack" folder icons and as long as the apps work, personally I would not bother past what you already know.
I have CC and folder icons display normally in CC 2018. If it is important, you get those custom icons and much more up to date features and functions by subscribing.
Beyond that, you can ask these Mac support forums:
or even Apple Support.
Best of luck -- Gene
Thanks... the funny thing is, I didn't have to use terminal to get it to install at all... The normal installer worked just fine!
Pre-Sierra days we could go into Security & Privacy and set Gatekeeper to allow all apps, not just the signed and app store ones.
Glad you didn't have to go this route: