The design of Gmail has been updated to match the design language of Material 3. It is said that several updates are planned, such as improving Gmail for tablet users and supporting emoticons. Most notably, the color has changed dramatically. The graphic technique used to separate the layers and express the buttons has a much lower contrast than before. Chats, spaces, and meetings, which were previously represented by moving to additional functions, have been expressed as the main menu at the top of the hierarchy and at the far left.

This is a very disappointing update. It is difficult to distinguish the fine differences between elements that are used previously and those that are newly added. The hue of the accent color used for various elements, such as the button to write a mail, the active tab in the left sidebar, and the mail checked in the list, is subtly different. It was hard to know what the purpose was in a way that didn't unify using the same hue, nor clearly contrast with distinct hues. Since the gray tone of the background color and the tone of the accent color are different, various interactions are not naturally connected. The color of the search bar and the read mail doesn't seem to be distinguished from the background color, which blurs the eyes.

More and Sources

https://blog.google/products/gmail/gmail-design-update/