Color shading can be just a matter of testing out. I would not do any color judgement over printed or screen viewed uses since they can distort shades. You are the first to be judgemental over specific RR color companies.
t-man is spot on with this... I bought the floquil colors that on the screen didn't look like they would match up... even when originally putting it onto the loco it didn't look right, but as it dried, it matched up.