I've found with Maudaie hybrids with mottled leaves that high light caused them to fade. I moved them from west windows to lower light north-east windows and they darkend again.
However I agree with Hedge, it could be either and you need to judge by where it is now. If it was going paler in a bright window, then dry a darker spot, however it it was going paler in a low light spot then try a brighter one.
Having said that I've also had one of these fade when it had root problems and was getting dehydrated due to root rot. Unfortunately it's a bit like a human looking pale... you know they are sick but can't tell why just from the pale look. It may be worth checking the roots, disturbing them could cause the flower to blast, but not correcting a problem in them could also kill the plant