Remember, sometimes the purple coloration of the stem/s is a genetic trait of a lot of different strains of Indica.

On another note though, it does appear as if you're over watering unless of course you took your pictures RIGHT after you watered. You should check your pH as well, especially if you're using an unknown soil...
EXP13 Reviewed by EXP13 on . Photo of 1st plant I planted this on 11/12, as of today it looks like this. Should I be worried? It doesn't appear to be growing up anymore, but it is growing bushier. My set up includes 2 40W/3400L T12 CFLs & 1 40W/2600L CFL in a closet painted white. The plants are almost touching the CFLs. Temp 78-80F. Crappy soil from Home Depot. Rating: 5