Invert colors?

in Questions
I am doing a piece that requires the use of inverted colors, I was wondering if there is a way that I can find the inverted color without having to pay for an outside program? Many Thanks
!!

Comments
It is possible to invert the colors through a bit of sorcery
You can see an example of how it can be done here:
https://pyxeledit.com/forum/discussion/comment/2395