I saw a site back then with female tracksuits recolor in the colours of the rainbow with some black parts. And there were other similar recolors (of other clothing), all in various tones of the rainbow. The site's background was dark.

First thing that comes to mind is this one, but it's probably not the one:
https://modthesims.info/d/375583/fi...-maternity.html

Any other information you've got to go on, like the timeframe on "back then" (a few weeks ago, or 5-10-ish years?), or more on the site, maybe the site logo, or something you remember about the creator/site (partial name/url/logos/avatar/etc,), or the general style (Maxis-match (textures), or more realistic)? Anything would be helpful, especially when looking for clothes, since there's a lot of it.

Searching sites are getting a bit less helpful with sites these days unless there's more to go on, unfortunately (they often keep coming up with TS3/TS4 searches), and there are a lot of old/dead sites all the way to 18 years back they're archived where searches can't find them, or simply gone.

I found it around 2019 and the texture was the same as the masix one but just different colours.

I found it

https://archive.liquidsims.com/mirr...t/clothing.html the second post