There is plenty of secrets in Crash Bandicoot 4, including some colored gems that you will need to find. These are hidden away in different levels, and you will need to keep your eye peeled if you want to find them.
You can find the red gem hidden in the N. Sanity Peaks level. As you run through the level you will come to a couple of phase-shifting platforms near the platform for the bonus level. Just past this is a set of stone steps, and on the right, you will see a small diagram carved in the wall.
It shows a grid of 9 blocks, with an arrow pointing to the bottom left block, then a path shown by arrows all the way around until you hit the center, never landing on the same block twice. In the next room, you will find some of the phase-shifting platforms laid out in a 3×3 grid, and you will need to copy the exact route from the diagram to unlock the red gem.
Remember, start on the bottom left, the move all along the outside until you get to the second line block on the left, then jump to the middle. It’s a little awkward to do, but once you get the platform timing down you will be fine. Our best advice is to ignore double jumping and just use a single jump, as it is much easier to keep the rhythm of the platforms when you do that.