I am a huge fan of the X-Men. One of the first comic books I recall reading is The Days of Future Past saga from Uncanny X-Men 141-142. Even as my habit grew and I collected other titles, I retained my love for the (not so) merry mutants. The appeal for me was that they were always on the run, always living life on the edge. Spider-Man may have rent and ailing family members to worry about but the X-Men were attacked by foes from the future, threatened by alternate realities, hunted by the government and at war with extremists.
The 20th Century Fox X-Men film series modernized the mythology of the comic book, often taking liberties with the source material but keeping the soul of the Marvel Comicverse while adding new elements that appealed to those unfamiliar with comics in general. It was a bold move but X-Men is the longest continuing line of movies based on comic book characters to date chronicling seven theatrical outings (if you count X-Men Origins: Wolverine).
The imaginative designs of the superheroes seen in print was stripped down to leather gear that bore only a hint at an X-design. In the year 2000, it was understandable as viewers were unlikely to accept colorful costumes.
However, with the success of several Marvel Studios films, the superhero costumes are now much more easily palatable to the average viewer. Clearly Fox was considering embracing the ‘yellow spandex’ that was once scoffed at as seen in an alternate ending to the 2013 Wolverine film in which he received a special package containing an outfit not dissimilar to the classic design.
A version of the yellow and blue outfit was seen in X-Men: First Class as well, but the series was still very self conscious of looking silly. Unfortunately, the Wolverine scene was cut which I think is a missed opportunity.
With the revision of the timeline in Days of Future Past erasing X-Men: Last Stand, the sky is the limit for the upcoming X-Men: Apocalypse. Perhaps we will finally see a blend of the colorful and practical designs, embracing the comic book origins of the X-Men.