This rather easy to do.
But first please lets test and merge #23095

@infograf768 may I go ahead with this issue ?

@hardik-codes Joomla! is is community developed software. You do not need to get permission to submit pull requests. Go for it!

OK
@Quy could you help me with the files to get started ?

@Infograf and @Quy which 2 icons need to be changed ?

Sorry I don't know. @acvmultimedia please advise.

The background can be modified by changing
https://github.com/joomla/joomla-cms/blob/4.0-dev/administrator/templates/atum/scss/blocks/_quickicons.scss#L60-L62

to

    &.success {
      color: var(--success);
      background: #d9e6d9;
      box-shadow: $quickicon-box-shadow-success;
    }

to get, after running npm ci

If we want to change the icons, they will be changed globally, i.e. whatever the status.
Example 'image' => 'fa fa-file-o', in:
https://github.com/joomla/joomla-cms/blob/4.0-dev/plugins/quickicon/overridecheck/overridecheck.php#L87-L96

can be modifed to
'image' => 'fa fa-file,
similar for Extensions update to obtain

Thanks @infograf768 that is the idea, I am a designer and no programer can you change it for me in Joomla! 4 core?

OK, for green background #e9ffe5 and icons better with interior filled with color (star and document).

background should correspond to the color we use for Success Messages, that's why I used
background: #d9e6d9; which is the same as used in alert.
No usee to introduce new colors imho

Sorry, it´s OK #d9e6d9 thanks @infograf768

Will make PR with a new $colors variable

@infograf768 please may I go ahead with this issue

Sorry, already done
#23733

Please test. Closing as we have a patch.

@hardik-codes
There is a quite simple way to find out where a code has to be modified:
Use web developper tools ( I use Firefox ) and inspect code.
In 4.0, a specific css may come from different types of scss.
To test I often put debug system on to test stuff on non-minified files.
Then search how this code is produced. I use often BBEdit multifiles search.

OK I will close Issue?

done