Google has a color selector among the many features in their home page. It’s free, works in any browser and it’s easy to copy color codes into Office.
Search for ‘Color picker’ or https://www.google.com/?q=color+picker then move the two circles to choose the exact color and shade you want.
The HEX and RGB color codes are shown at left.
Modern Office accepts the HEX color value. For earlier Office versions, use RGB.
The RGB value can be used in any Office color selector on the Custom tab. Enter the three numbers into the Red, Green, Blue boxes.
As you can see, Office itself has a color selector but the Google one is larger with finer graduation. There are many other color selectors, the Google version is available on almost any computer and free.
The CMYK value is handy if you’re getting the document professionally printed.