How can you change text color settings in Visual Studio 2019 to match the style of VS2017?

You can revert to the 2017 style by disabling Tools > Options > Text Editor > C# > Advanced > Use enhanced colors for C# and Basic.

I don't have 2019 to see what the differences are, but the approach I'd take is to have one person go through the process of customizing the colors to 2017 ones, then export the settings to a file that your peers can then import (in 2017 this is under Tools > Import and Export Settings).

I'm curious why you want to see a specific color theme across the team.