Accelerate crossing back rings (6th level rings)

In my experience :
1. Use light /whitish coloured gravel/ bottom
2. Do not put lamp on top of the tank , instead put lamp on the bottom of it.
3. tanning , tanning and more tanning

In theory , to adapt camouflage, the fish will follow the colour of the river to cover it's appearance ,so most of them will get it's back's rings dark coloured , even when they were adult size crossback SR will have their back's ring darker core than the rest 5 level rings.
Try to manipulate the bottom colour to accelerate crossback process, remember Bloodred are faster in crossing back rings than Chili Red