If you want your colors to be dead-on, here is a chart of all the official colors used by DRG/DR/DBB/DBAG/OBB/SBB with - this is HUGE! - RAL codes, which can be looked up for RGB or Hex equivalents. https://de.wikipedia.org/wiki/RAL-Eisenbahnfarben So, for example, Traffic Red (Verkehrsrot) is RAL 3020, which is represented digitally by RGB 187, 30, 16; Hex #bb1e10; and HSV 5, 91, 73
Does any of that translate to the colour system DTG has implemented? Because it is neither RAL, RGB nor Hex in the livery editor.
There are any number of online conversion pages that will turn RGB or Hex codes into the HSV used by Livery Designer. Or you can use a graphics program like Photoshop or GIMP for the conversion, since they implement pretty much all the various digital color-specification systems.
Unless you are a poor console player.....lol then you may as well do my method. I hold a photo of the train on my phone up to my tv and eyeball it until they look like a match!