I was trying to be funny, but the 2 are related as in they are opposite cases of the same underlying phenomenon.

The sticker itself is red, so the joke is saying you must be travelling at some fraction of the speed of light to see the sticker as red and if you were going slower it would appear blue.

I’m not sure if you actually understand it and just did a brainfart while typing, or actually don’t understand it well, so I’ll just explain…

• In both cases (redshift and blueshift), you need to be going fast enough relative to the sticker for either of them to happen in any noticeable way. Although it still happens even if you are going only 1 cm/s
• The sticker is red and you will see it being red if you are not moving relative to the sticker. i.e. if the car is parked and you are just standing behind it, it will be red (don’t take my word for it. Go stand in front of a red thing and look at it to find out that you see red colour)
• If you are going away from the sticker, you will observe a redshift. And since the sticker is red (let’s assume for simplicity that it is the reddest of red (whatever that would mean)) the redshift will make it go infrared and hence you won’t be able to see it with human vision.
• If you are going towards the sticker, you will observe a blue shift and you can use the crude, but useful VIBGYOR to deduce that if you are not fast enough to see Blue, you can expect to see either of Orange, Yellow, Green.
• This effect is similar to the phenomenon that occurs to sound. i.e. when a car comes towards you with the horn continuously blowing, you will hear a higher pitch and when the car with the horn blowing is going away from you, you hear a lower pitched horn sound. The reason this is more easily observable with sound, is because sound in air is slow enough for us to notice this.

Bonus: I was playing the game X4: Foundations and realised that they actually have simulated this effect in the in-game sounds, which was an impressive little detail and I loved it.