Source that Epic did this?
They used to, idk if they changed it now but to give an example, the purchase page would be color coded based on the most visible color the game was showing, a walking sim in a jungle would have a prominent green and brown in its game, so the checkout page would be green + brown letters
Thought it was made to keep consistency to "don't take you out of the game" with a standard white and black screen, but being kids involved it could work exactly to entice them to expend more money