One of the biggest and drastic changes to the looks of the new 2021 M1 Apple 24-inch iMac, aside from its colour options, is the fact that Apple has decided to make the Bezels white.
The last Apple iMac to feature white bezels were the G5 generation, which came to an end in 2007 after being replaced with the highly recognisable brushed metal and black bezel iMacs.
Apple has undergone a drastic change to their marketing strategy in recent times. They done away with their professional look and strictly exclusive branding and offerings, replacing that with more vibrant and "self-expressive" products. They have also paid homage to their G3 generation of products too, which also featured a variety of colours and extras.
The change from black to white bezels in the new iMac serves many practical and aesthetical purposes, the main one being for the new iMac to blend into its environment. Previously, the iMacs were marketed to professionals, such as video editors, who usually worked in darker environments. With the new iMac, however, the design team worked out an average of who their target market would be, and decided on a neutral bezel colour that would not be an eye-sore in most cases. They then decided that a very light neutral grey, that is borderline white, would be the best possible solution.
Take a look at the video below by the YouTube channel, Apple Explained, on Why The New iMac Has White Bezels.