(in)elegant weapons, for a more civilized age.

chroma.sh

#!/bin/bash
# chroma by Karim Vergnes <me@thesola.io>
# License: WTFPL 1.0
# Requires xrandr to work. 

# Display to modify
: ${XRDISP:="eDP1"}
# Speed at which to alternate colors
: ${COEF:=1}
# Intensity of result
: ${MAX:=100}


xrandr_color_shift()
{
    xrandr --output $XRDISP --gamma $1:$2:$3
}

# Increase factors
rinc=$COEF
ginc=1
binc=-$COEF

red=1
green=1
blue=$MAX


trap "xrandr_color_shift 1 1 1 && exit" INT

while true
do
    xrandr_color_shift $red $green $blue
    (( red   += rinc ))
    (( green += ginc ))
    (( blue  += binc ))

    (( red   >= $MAX )) && rinc=-$COEF ginc=$COEF  binc=0
    (( green >= $MAX )) && rinc=0      ginc=-$COEF binc=$COEF
    (( blue  >= $MAX )) && rinc=$COEF  ginc=0      binc=-$COEF
done

Just cycles the gamma on the selected display. To change the intensity, add a MAX environment variable. The COEF environment variable changes the step (the higher the value, the faster the colors will cycle)