Ah, largemouth, Mine looked just like that when i first got him and they start to lose the coloration. Dark now, later he will be "whiter" due to the water being so clear, and not enough darkness. I have found when the lights are off (1am) he will turn dark again. Mine is not going fast, hes in a 75 still. Have not got my 150 yet.
My bass is on pellets, for the first month i was feeding him plump minnows, For about a week he would not eat, I have found out that if you are going to get 2 get in now or he will kill it off.Ok i have also found out that if you feed him ghost shrimp they cant resist them, he should take them the 2nd day. Now the hard part, heres how i did it to my bass always kept food in his tank for a month, I let him kill them off (eating them) then i gave him different choices tialpia was one crawdads. Then i fed him once in a while dropping shrimp pellets in there would eat them but spit them back out. Then one day he killed my 5in tialpia and then started to eat pellets. Now he eats from the top to. Start with sinking pellets.
I would feed him live stuff till he get settled in, and use to be in a smaller space. I can take pics later. I have a armored cat in there hasnt killed it yet. My poor tialpia was growing strong out smarted my bass for 2 months. He was only 1in when i put him in there. Made a hole in the sand under my aerorater thingy lived there 2 months then got balls and started swimming around all the time. Bass was hungry tried to eat it but was unsucessful. Killed it though. I think my tilpia taught my bass to eat pellets

Be prepared only have 1 fish in that 150. Bass are very mean.Good luck let me know hows he is doing.
Sorry about my long story, Im at work and bored