About color : there are big issue with usage of text-success and text-info with a lot of admin or Fruity template …

Yes, you're right. If I recall right, for example some warnings are in red, some in green. Do you already have a list of points that could be changed?

No sorry :)

I must check , come back here when it‘s done

Same issue in 3.X :

1. text-primary and text-info and text-success are near same
2. difficult to tell if bg-primary is success or not
3. btn-primary and btn-info and btn-success are near same
4. Success row show bigger (issue in statitictics.css)

Some other issue

See https://gitlab.com/Sondages.Pro/checkAdminBootstrapColor for view sample

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Why success of Bay of many is blue ?

In home page settings, those are switches. In the global settings those are buttongroups.
I would back your proposal to use a dark shade of the main color as a background for the selected option.
This has to be talked about in the team, though.

The LimeSurvey color scheme is based on a monocolored scheme, meaning success and primary are the same colours, and Info being a gradient of that color.
This was so since LS2.5. It is also repeated in the fruity themes based on the backend colors.
We won't change this in LS4.

meaning success and primary are the same colours

But why remove a colour of Bootsrap ? Succes and primary didn't have same meaning …

Ok, but still : no difference between success/primary or danger/primary make it very complex to use …

See for sample
bootswatch Journal : primary red, danger orange
bootswatch Cosmo : primary blue, info purple
bootswatch United : primary orange, danger darker red

And still :

1. table Success row show bigger (issue in statitictics.css)
2. Why success of Bay of many is blue ?

Because :
The LimeSurvey color scheme is based on a monocolored scheme, meaning success and primary are the same colours, and Info being a gradient of that color.
Also this is the scope of a new ticket.