Did you literally use ~
as the start of the path in the Startup Applications
GUI? That's fine for the terminal—it will fill in /home/nosnahc
(or whatever your home directory really is) for you—but, for the startup applications, you need to specify the path in full.
Try:—
/home/nosnahc/Application/legion-kb-rgb set -e Static -c 200,150,0,200,150,0,200,150,0,200,150,0
changing your username as necessary.