Touching colors must have a minimum 30% grayscale differential (contrast) or the human eye struggles to find the edges. This retinal error can cause an optical effect known as popping. This color “secret” is not generally taught in design schools.
There is a so-so online grayscale test site:
Try it. It doesn’t always work on every site. I do my tests in Photoshop with screengrabs. No particular reason. Habit?