X today started giving a blue tint to accounts that have a number of followers whose identity has been verified. This means that this account receives a free Premium subscription for having followers who pay for a Premium account.
Currently a free Premium subscription with a blue smear is given to accounts with 2500 followers who have verified their identity. Meanwhile, Premium+ subscription is given to users with 5000 followers whose identity has been verified. The announcement of the blue coating was made by Elon Musk on March 28 but was only activated today.
X used to be Twitter throwing a blue smudge on legacy users who received it before the site was taken over by Elon Musk. This action received a negative reaction for causing the dumping of purchased blue smeared accounts.