So, basically, to accommodate the colorblind users to the max extent, we are supposed to drop all colors but blue...

And also, the Orange color or the Red color is apparently bad for buttons without any statistical data while the experiments that other people actually did show otherwise.

https://blog.hubspot.com/blog/tabid/6307/bid/20566/the-button-color-a-b-test-red-beats-green.aspx

https://dominoconnection.com/color-buy-button-use-sales-page/