Couple things. Highest THC comes when almost all of your trichomes are cloudy. The cloudy color indicates it contains THC. Highest THC is not necessarily best, however.
When the trichomes turn amber, this indicates a THC breakdown into other cannabinoids. These other cannabinoids have wonderful effects. If you want hard hitting, catatonic inducing highs, wait for 50% amber trichomes. If you want a mellow high, go 30%. An energetic high, 20%. Most THC, probably around 10%. Also go by trichomes on the buds, not the leaves.