Im not sure if this is an option in the game already, I have been unable to find anything on JP servers.
But it would be nice to have the ability to change the color of enemy spell telegraphs. For example when facing the menacing castle, There is a lot of red on the screen, The castle has a beam that shoots across the field that stuns you and combos into another beam. I find it very difficult to see the initial telegraph. Green / Blue would be great options.