Script to add red tint to the entire screen.

calib.sh

#!/bin/bash

# Call with a percentage value from 0 to 100
# 0 means only red, 50 means half of green and blue is shown through
# if you don't give any arguments the calibration is cleared

if [[ -z "$1" ]]; then
  echo Clearing all calibrations
  xcalib -clear
else
  FILTER=$1
  echo Setting FILTER to $FILTER
  xcalib -clear && xcalib -green 1 1 $FILTER -blue 1 1 $FILTER -alter
fi