I'm adding this YouTube posted guide here as a possible solution, because I've seen answers to my similar posted question in the header that assume the question was about the "Start Menu" color that are now "locked"; but this is about the pre-startup OS option menu color that can be lost if one make changes using Bcdedit as I did, where I lost the colored background for my Dual boot Windows 10 environment.
I'm also adding this EasyBCD solution I found in an earlier post with an updated link: "You can install EasyBCD from here: EasyBCD , and on Edit Boot menu tab change it to the Windows 10 bootloader to get the nice blue one instead of the DOS-looking black one."
So I hope this all helps, YouTube link is below image.
https://www.youtube.com/watch?v=gtc5yTRV9iI&t=6s