Please, is there anybody able to create a mod to prevent townies from wearing pink, blue, green hair at random ?
I hope this is the right place for my question.

best regards Trixie

Are you using custom hairs? I've been looking through the CASP files for hair while I've been defaulting their colors (I don't like banana yellow for blonde, I'll admit it), and so far, most of the default EAxis hairs are disabled for random--meaning townies won't spawn with them and they can't be inherited. Thus why children won't grow into the same hair color as their parents (if said parents have unnatural hair colors); not only are the colors simply unavailable for child Sims, but you'd have to change the CASP files for the unnatural colors so they can be inherited.

However, most custom hairs I've used have all the colors enabled for townies and for genetics, though these hairs also aren't using the proper hair color flags. But that's an unrelated issue to your question, so I won't ramble on about it.

If you are using custom hairs, it's pretty easy to edit what you want for your private use. Just keep in mind that disabling it for townies also disables it to be inherited. All you have to do is:

1. Open the file in s4pe
2. There may be a lot of instances in the file if the creator merged all the colors into one package. Most likely, the CASP files will still have the color's name, though, so theoretically, it should just be a matter of trial and error of clicking until you find the color you wish to disable. (The CASP file is the one with various text, with categories like Version, TGIoffset, PresetCount, Name, etc. You can double-click it to check its file type if in doubt.)
3. Once you've found the CASP file you wish to edit, while it is selected, open up the Grid, which is on the bottom of my UI. A pop-up box should come up that says Data Grid.
4. Click the Expand All button, then navigate down the list (somewhere towards the top, usually) until you find ParmFlags.
5. Branching off from ParmFlags will be several True/False settings. You want to find AllowForRandom to set it to False.
6. Commit and repeat these steps until you've altered all the CASP files you want.
7. Save your file. You're done!

Hope this helps. If it is an EAxis hair that has been spawning on your townies, mind describing which one/ones so I can take a look at it?

Surely you need s4pe for this which can be found here:http://sims4group.github.io not a Sims 2 package editor? Because, if SimPE worked correctly for Sims 4 there would not have been any need to develop s4pe would there?

lol, that was a typo. Sorry for that. Yes, you would want s4pe.