Not all purple is faked. All onscreen purple is fake, but so is onscreen yellow and orange.

Indigo and violet are real and look purple to us. This is because they are moderately close to the blue frequencies so stimulate our blue cones and moderately close to double the red frequencies, so also stimulate our red cones.

There’s no way for you to tell whether you’re looking at something that’s genuinely reflecting indigo or violet light into your eyes, or something that’s shining a mixture of red and blue light at them.

If it’s on a screen, it’s definitely fake and not indigo or violet at all. Screens can only make red, green and blue light.

Any yellow or orange you see on a screen is also completely fake. It’s just red and green light mixed up with no yellow at all.

If you’re seeing it on an object, it’s far more likely to be real yellow or real indigo/violet. Pigment and light don’t mix in the same way at all.