thats not good advice, he was right in saying that they get the last bit of color near the last few weeks of flowering though...(usually in the last 2-3weeks of flower)
If you would like a purple color its best so start with a strain that turns a purple color. If you would then like it to be more colored by temp changes (which do really nothing for the bud but make it grow worse because of low temp conditions)
The best way to do that is to lower the daytime temps in the room to around 60F. Then @ night you want it to drop 10 to 15 degrees lower than the daytime temp to a temp of 45F-50F
I would actually suggest finding better genetics though for the best purple colors without having to screw around with temp changes. Having a cold or hot room lowers yields terribly and is actually the most common factor for low yields.
Im growing this strain out in my room now, it got this purple in a room that was 78 degrees Fahrenheit.
Pm me if you want more info on this general subject or the strain Im growing