Nice set-up. Looks Great!! I would not plant too heavy--pruning and pulling plants will mix the gravel. Stay with maybe a few plants, but bigger ones (6-7 large swords??).
as far as keeping the color seperation ive found it to be pretty simple. once the hardscape is complete i will add another 1/4- 1/2'' of substrate & just enough water for the substrate to tighten up. i will then add all the plants from moss to stem plants do the minor touch up to the substrate as needed allowing about a 1/2 hour for the touched up substrate to tighten up from the moisture allready present. at this point your ready to start filling the tank slowly. i do not prewash any of my substrate and only experience very minor cloudiness after filling. this tank will be getting a pretty heavy planting but many will be fairly compact(a lot of moss). lol pruning and regular maintanence is a bit easier for me than most in a tank this size, at 6'6'' my reach enables me to get to everything with relative ease. a little hint to the stocking list, there upper water column will be inhabitted by a very large school of galaxy rasboras. rather than going with larger fish in a tank of this size as most people do i want larger groups of smaller fish as they are found naturally.