Liliana,
I can understand your concern about strip colours.I was trained in the blue-outbound,yellow-inbound mode.I then worked abroad and it was the complete opposite,and very confusing.I would stick with blue-outbound,yellow-inbound and pink for others.Red for runway blockers.Simple and effective.
I would go with the highlighters,or coloured strip holders.Even writing something on the strips would be useful.You can get strip holders with springs in the back.It makes strip loading and unloading a breeze.