if you have an older lcd screen you bought from adafruit basically there are certain colors that only make it bright. If you look at what is going on in the imported packages you're using for your code there are colors you might be able to trigger the hex value you need for a bright screen. I had to do a bunch of different things to make my screen bright and a lot of it may depend on the modules you have in your libraries folders and what that stuff is doing and if you have imported those packages into the code as like sub code unseen in your main .ino
i think 330R's advice is superior but you may find you can solve your problem with code.