They smell like plants or weed? I cant imagine that plants that age give off any odor... but whos knows i've yet to see it all!
In regards to the purple leaves, i noticed that as well but mostly on the stems.... The only time i had leaves purple was when stress was high. My fimmed plant went all purple with the new growth, but then back to green in a few days.
Good luck with your setup, and if i were you, i'd try to add more wattage for 4 plants. Hell, im runnin a 400W for only 2 plants!