I believe the topic related to prepositions are one of the most difficulties to explain.
[The sky is pink on my computer.]
According to prepositions usage, one of the many other uses of "on" is to indicate a device or machine: on the phone, on TV, On the computer, etc.
>> I have been on my computer for hours.
>> She is on the phone.
>> My brother is on TV tonight.
>> That actress is on the TV.
You wouldn't say "That actress is in TV, because she's not really inside your TV, in fact, she's on the screen.
In case of computers, we can also use the preposition in, however, in this case it indicates there is something inside the hardware. If you hid something like a toothpick inside a computer itself, you would say "The toothpick is in the computer." because the physical object is inside the computer.
When it comes to data or something like that, you refer to it as "The file is on that computer." This is because there's no object that you can hold or touch; you wouldn't reach INTO the computer and pull the file out, you have to use the computer itself to access the data that will show you the file on the screen of the computer:
>> Data is stored on the USB drive;
>> The USB drive is in the computer.
>> There are cables in the computer that allow you to access the file that is on the computer.
I hope I've helped.