I observed that on Windows 10 the following settings can match the Start Menu color with the Taskbar Color:
1. Set the Taskbar color to Auto (that is, follow wallpaper's dominant color)
2. Switch to Smoked Glass skin in Classic styles and make sure "Reduce glass option" option is unchecked.
3. In the search box of the Classic Start Menu Settings window, type: opacity.
- Set Glass opacity to 30
- Set Taskbar opacity to 80 (This is of course assuming that you are using a glass taskbar which you can set from "Windows 10 Settings" tab).
For Windows 7 style or if you are using the opaque taskbar with an opaque skin like the Metro skin, there is a skin:
http://www.classicshell.net/forum/viewtopic.php?f=17&t=4934 that uses $SystemDarkAccent3 color which is the same as the taskbar when it is opaque. You could port it to Classic style.
You can get the full set of Metro colors by downloading and running the Classic Shell Utility with the "show colors" parameters:
http://www.mediafire.com/download/3ukeryzw41qpfz8/ClassicShellUtility.exe e.g. %tmp%\ClassicShellUtility.exe show colors