There are different types of browser add-ons that you can use to customize the appearance and layout of your Gmail interface. One good example of this is Gmelius . While the features of the said extension are a lot more advanced, it cannot add colors to Gmail’s usual black/grey inbox icons. If you wish to do this, then you’ll need to follow the steps listed below.
How to add colors to Gmail’s usual black icons
On your Chrome web browser, go to Web Store then download  and install the extension called “Color Icons for Gmail”.
Once installed, type chrome://extensions on your browser’s address bar then press “Enter”. You will then be able to view the full list of extensions that you’ve installed on your web browser.
On your browser’s extensions page, find the section for “Color Icons for Gmail” then click the “Options” link right under it.
The available icon sets for the said extension will be displayed in a new tab. All you need to do is to pick the icon set that you like. As of now, the extension offers a total of three icon sets. It’s up to you if you want to choose the Keve’s Black set, Keve’s White set or the Silk set.
The Silk set has the most number of colored icons.
Open a new tab then log in to your Gmail account. If you are already logged in, simply refresh your Gmail page to apply the UI changes that you’ve made.
So there you have it. You have successfully learned how to replace your Gmail account’s usual black icons with more colorful icons.
Just remember that the color of the icons will return to their original style if ever you decide to remove the Color Icons for Gmail extension from your Chrome web browser.