I have Version 11.2, Build 27.1 in Windows 10 (1903).
I was able to add colors through the "Options / Color Palette" page. I'd type in a Name, then click on "New". I'd enter the RGB numbers I wanted and OK & OK. I now have that color/name listed. If I start a New from Scratch drawing or open an old drawing, it has the new color listed in Properties, though you may to restart TurboCAD.
If I have a lot of colors to be added, I would set them up in a [Color_Palette] file, then use the TCExplorer Palette to bring them in to the program. Keep the RGB sequence; RGB68=…, RGB69=…, etc.
Expand "Settings", then "Built-In(Current).
Scroll down and right-click on "Color_Palette".
Browse for the "Color_Palette" file that you updated with the new colors.
Click "Extract". All the colors in the file will be listed in the window below.
Since I have all the colors I want listed in the file, I use "Select All", then "Replace All"…
then "Add" and finally OK.
You may need to restart TurboCAD or just a New from Scratch drawing to see the new colors.
Hope this works for you.
Designer, Deluxe, (Professional, Expert, Basic), Platinum
Windows 10 Pro (1903), 64-bit