I don't know when exactly the change was made, it could sometime between 28th Feb and 1st Mar 2025
It is still 1st Mar 2025 for those in the western part of the world but as I just checked now, iCloud.com no longer shows white icons while on dark mode. A few days ago, it is still showing white icons while on dark mode. I am just using iCloud.com and not the beta website so if the change was made earlier, it seems to have just been applied to the non-beta version later.
Even the newly introduced Invites app has a dark icon.
It is still 1st Mar 2025 for those in the western part of the world but as I just checked now, iCloud.com no longer shows white icons while on dark mode. A few days ago, it is still showing white icons while on dark mode. I am just using iCloud.com and not the beta website so if the change was made earlier, it seems to have just been applied to the non-beta version later.
Even the newly introduced Invites app has a dark icon.