Using MS Paint I was able to find the RGB
Thank you Kevin.
1. Take a screenshot (Alt+PrtScn) of a Tableau viz using the color palette.
2. Open MS Paint (available on most PC's with Windows).
3. Paste. Zoom to larger size under view.
4. Use the dropper icon anywhere on the color you want.
5. Go to Colors, edit Colors, Define Custom Colors... in the RGB, write down the numbers.