Hi Duane
You must have received the 1903 feature update . ..
Open the Settings App (gear icon on your Start Menu)
Go to Personalization - Colors
Set 'Choose your Color' to Custom
Set Windows Mode to Dark
Set App Mode to Dark or Light
Then that option to change the Taskbar color should be active . ..
You can also set App Mode to light or dark separately form Windows Mode and there is a new feature in 1903, where form each Apps settings, you can individually set an app to either dark or light mode . ..
.