Since most or even all of them are publicly traded companies it isn't that difficult to find out.
Walmart had a net income of 14 billion, they have roughly 2.1 million employees, that leaves each employee with an additional 6.6k for this year or roughly an additional 550 a month.
Doesn't sound a lot but that can be done without impacting any other business practices. And for some of the employees overseas that might be doubling their salaries.
That might not be true. They have more receptors for color but tests indicated that they are worse at differentiating colors than humans or other animals. They could only differentiate wavelength of 25 nanometers apart while humans can do it between 1-5 nano meters.
Also being able to see a wider spectrum might be terrible with all the light we use in electronics.