Can you post tank's photo? So far I found very few photos, and in none of them fish kept its color.
Mine started to change color to much darker, muddy color (within 10 days, BTW) - tank had black background and equipment. Moved all in anther, unpainted tank, with background of red mylar and two plastic red corals, later will add corals, it still QT:

Low light for a couple of days to let it become familiar with new surroundings.
Fish tries to move either away from light, or prefers black plastic of equipment. Swims time from time, a lot, catching water by opening mouth and expelling it through the gill openings, that positioned behind back "legs" and look like jets of airplane. Mechanism could be different, but impression is very strong.
It seems, that it will be a problem: swimming from top to bottom and back again, facing own reflection in the glass, not covered by background. Have no idea how to prevent this, apart from adding photo background with print on it, and they are not available in reds. Textured aerosol paint, stone-like, again is not available in red colors, and tank is already set - no aerosols inside this room.
Apart from fighting with keeping color vivid, so far it is very interesting, low maintenance fish: feed once a day from fishline in rigid airline tube, change filter pad every second day, siphon bottom weekly during partial water change - it's all. Poop is a compact piece, less than astrea snail makes.
When wave the food before it (still "It", no name yet), it waves the lure, attracting prey. Family members add, that each of us thinks than fooled each other

As I understand, I was lucky with this fish, that did not require weaning at all and started to eat frozen food (PE mysis) by itself. Most posts about frogfish say about their - especially wartskin and dwarf tuberculatus - refuse to accept dead food.
Is your brown fish painted frogfish too or hispidus? I have seen them once in LFS, but they said that it will grow to 1 ft/30cm size
I still curious, how the multiple frogrishes are kept: Rene and Uberfugu have them, LisaD too, if I remember right, but no photos of how the tanks are arranged for convenient access for maintenance. If you will see something on the web, post a link, OK?