To add a bit to lemonslice's recommendation, I would create a .desktop file linking to the script. Then add it to your startup via the System Settings. It works perfectly for me. Here is an example of what I've done...
create a new text file and add the following:
xcaliber --bR=256 --bG=256 --bB=212 --gR=1.04 --gG=0.9600000000000001 --gB=1.01
Save as display.sh or something like that.
Then in the terminal navigate to the folder where your display.sh is saved and run the below command in the terminal:
chmod +x display.sh
This will set the script as executable.
Now you need to create a desktop file so we can add the script to your startup. Open a new text file and name it something like xcaliber.desktop.
add the following to the file:
Name=Display Setter Application
Comment=A script to set xcaliber settings
Exec=/path/to/display.sh //obviously here you want to add the true path to your file
Icon=/path/to/icon.png //and here you want to add the true path to your icon file if you want one different from the base gear
Once that is done open System Settings > Applications > Startup (I think that's what it's called) and add your xcaliber setter application.