Colors Tamil got benefit only due to Naagin 2 as the show was already popular due to Sun TV. Once that ended it fallen down.We can trust this source as they are giving it from a long time and others sources also sounds same(Atleast the order of positions are believable). Zee isn't became consistent in that place and is randomly placing in 6,7 or 8th position. Anyway unlike Colors Tamil(entered Top 5 quickly and fallen) Zee is slowly building up their ratings. Thus it will be strong and they will not fall down suddenly.
Coming to Zee keralam. Zee really took good efforts for channel launch cause even at launch they launched programs from 6.30 pm( quite early for newly launched channels).
Even after initial failure they continued to invest good in channel. They invested more on good serials (if I am not wrong maybe with already popular actors) and not to mention SRGMP.
If they continue to invest good in fiction and nonfiction along with investment in popular movies, they'll surely have success.