>>55495701They're not meant to be that vibrant, they were oversaturated to compensate for the shitty GBA screen.
FFTA was one of the few games that actually had an option to change the colors for if you were playing it on a TV and set the colors to display as they were intended to be seen.
Some GBA emulators include shaders based on these options that let you make every game look like the FFTA TV colors option.