LEGO comes in many beautiful and vibrant colors. I have LEGO from the 70s that is just as bright as if it would have come from a set purchased today.
LEGO won’t get discolored, nor would the colors fade, if you keep one thing in mind; avoid strong light!
If LEGO gets exposed to direct or strong indirect sun (like midday sun through a window) on a regular basis, it will eventually get discolored. Discoloration can also happen from artificial light that is too bright and too close to your display.
This will especially be visible on white and blue bricks. (White will turn yellowish, and blue a brownish dirty-blue.) Look at the bricks below; all 3 of them are white, but the middle one was exposed to too much sun!
So, if you are planning to showcase some of your Lego collection on a shelf, or other open area, make sure the location won’t get exposed to strong sunlight any time during the day. And any lamps and other artificial lighting should be soft and a few feet away.
Although my room has lots of windows, I have my LEGO displays facing North, so even with the curtains open, they are never exposed to direct sunlight.
If you are displaying your LEGO for long periods of time, it is also a good idea to check on them every six months or so. Remove a couple of bricks and see if you see any difference between the sides that have been exposed to light, to the sides that are touching other bricks.
If you see any discoloration, change the lighting or relocate your display to another location. Or, just take it all apart and build something new! 😉