Discoloured duofold

[Cremator]

Hi I have a duofold fountain pen 2006 and it seems to have discoloured i have used it nearly ever day since owning it from new.i have just purchased a rollerball which was second hand and it is a 1996 and it seems much whiter than the fountain pen is this normal or is the roller ball a fake or as it just not been used much any help would be great please