This is a weird one.
I'm not "old" old yet (only 31), but I try to do things to try and keep my aim sharp (even though I'm only an average aimer). Sometimes in a game I'll try to focus more on the enemy model than the crosshair, and others I reverse it (though I find it causes more eye strain when I'm consciously focusing on the crosshair - anyone else get that? It can almost seem blurry, like the crosshair is on a higher up layer).
So I remember back in the cs days, it was easy to lose your crosshair in the sky on some maps, so I made a set of aliases where when I scrolled my mousewheel, my crosshair would rapidly change color. I wanted to see if the same kind of effect in QL would help me to focus more on aim, but without consciously staring at my crosshair.
For my purposes, I just alter my binds for strafe left and right to add an extra command in there, which will change the color and rotate the bind. Here it is if you want to try it out. It's probably wayyyy to distracting for most people, but so far I really enjoy it.
// the main cmd you vstr to change the color
set xh_change "vstr xh1"
// the 8 change commands that rotate what xh_change does
set xh1 "cg_crosshairColor 1;set xh_change vstr xh2"
set xh2 "cg_crosshairColor 2;set xh_change vstr xh3"
set xh3 "cg_crosshairColor 5;set xh_change vstr xh4"
set xh4 "cg_crosshairColor 8;set xh_change vstr xh5"
set xh5 "cg_crosshairColor 9;set xh_change vstr xh6"
set xh6 "cg_crosshairColor 12;set xh_change vstr xh7"
set xh7 "cg_crosshairColor 16;set xh_change vstr xh8"
set xh8 "cg_crosshairColor 21;set xh_change vstr xh1"
// use your normal strafe keys, or bind to something else
bind s "+moveleft;vstr xh_change"
bind d "+moveright;vstr xh_change"