From the Google Docs toolbar, select Fill Color (dipper with drop icon). You may need to hit the three-dot icon first to see it. Choose one of the suggested options, add your custom color ...

Since there isn’t an actual border feature in Google Docs, you can add objects ... Below the Tools tab is the Border Color option. You can click on it and add the same or 4 different colors ...

Google is making a small but profound usability tweak by adding an eyedropper tool to the color picker in Docs, Sheets, Slides, and Drawings. Today, the color dropdown in those four apps is split ...