as far as i understood it from a couple of horticulture texts...ALL marijuana plants are technically purple...
when chlorophyll works and captures sunlight its green, when xanthophyll captures sunlight its purple. ALL cannabis plants have xanthophyll in them, they are simply covered up by the chlorophyll, therefore all cannabis plants are purple, the ones that turn up not purple are covered up by the chorophyll green.
the ones that come up purple can be bred this way by manipulating the chlorophyll, causing it to die off through time and evolution you can someone can produce a stable purple strain...although, it can be caused by multiple variations for example nitrogen deficiencies can cause a plant to loose its chlorophyll or manipulating the temperature difference from day to night at a bout a 30 degree difference. This drop in temperature kicks the plant in gear sending signals to it to wipe that chlorophyll away and bring out the xanthophyll causing purple because to the plant the xanthophyll is like it's emergency secondary backup system that provides the about 30% of the plants energy
but just think for a moment...if you're growing a plant that is not bred specifically to be purple then i woudn't forcing it to do so take away from the plants potency potential?...The plant's energy gets turned into resin. That would leave me wondering how much more potent my plant could have been had i not killed off that chlorophyll... That's wasted energy that could have gone to more resin production (hence, more THC) Something to think about when desiring the pretty purple color.
here's a brief description of xanthophyll so you can see how it works in all plants.
http://jxb.oxfordjournals.org/content/early/2011/12/07/jxb.err362.abstract
As for the flusing....if you are using 100% organic nutes then there is no real need to flush. It's kind of impossible to flush when using organic nutes because organics break down in your medium...they gotta work harder than the synthetics in order for your plants to get the food but once broken down your plant takes what it needs and never too much, which is why it's hard to burn your plants with organics. There should be no salt build up for you to wash away with organics but be weary of what is marketed as organic, sometimes the organics tend to be not the best quality of nutrients or lack important things like Nitrogen.
I use both organic and synthetic. If you need a good organic line to use, give Earth Juice a shot. I got good results from it. hope this rant helps you out any because I just realized this response has taken me 20 minutes to type out to make all my thoughts make sense and flow together lol :no:
good luck if this is your first grow