If you haven't already started flowering your plants, your easiest route IMO, if you have the space, is to take a clone or two from every plant, then after you flower out your plants, and it turns purple (assuming one does) you already have clones ready to go for a large purple harvest
Hashtro is 100% right. Dont wait intill its in flower, take the cuts now and label them. You can do it the other way, but its much smoother sailing if you take the cuts now. trust.
about purple,
sometimes a plant will be purple from the start. it turns purple from the inside out. Other purps are the oppisite and usually has to do with the temps it was grown in, not so much genetics.
i agree, taking cuts
now is the safest way to ensure the
genes aren't lost. ...i agree with
ojd also, but if you're a
noob, revegging can be tricky, and the deeper into flower
you are before you take cuts, the longer it takes too root
them, and your failure rate will increase as well.
keep in mind that tossing useless clones in the compost
bin is way easier than trying to root cuts that have been
in flower for 4 or 5 weeks.
and
livinglegend is also right that many strains will display
purple under the right conditions.