These are steel replacement start buttons for the N64 controller.
They are machined out of steel bar stock and finished in a variety of temper colours.
This finish is also sometimes called heat anodizing and is achieved by slowly and evenly heating the part to a specific temperature after polish. The strong colour comes from a very thin oxidation layer on the steel and depending on where in the range it is can be somewhat affected by oils from fingerprints.
Generally deep blues and purple are the most touchy in this regard with the other parts of the range being more stable.
The button in the center is untreated steel to give a better impression of the colour change across the range.
These buttons are the same height or slightly higher than a stock start button and simply serve as an attractive addition to customize your controller. Functionality should be identical to a regular button but may be somewhat affected by the extra mass of the button material!