Mine gets Tetra Betta flakes, and once a week frozen bloodworm, and mashed pea on another day. He used to get Hikari bio gold pellets at his evening feed, but he suddenly started spitting them out and begging for the flakes which he eats with great relish. He also doesn't like daphnia, he spits them out.
I feed Tetra Pro to my community tank so once I gave my betta three flakes, one of each colour, to see if he would eat them. He ate the red and yellow ones but wouldn't touch the green. So do the green ones not smell nice, does he not like the colour (though he does eat peas), or is it because the Tetra Betta has red and yellow bits and that's what he's used to?