More as a point of reference for colours on t-shirts than for anything else – because these colours look different on RB tees than they do in our original designs.
This happens because the “display” colours are altered by RB to more accurately represent what the “printed” colours will actually look like.
This is of course a good thing.
Using this colour chart [you should probably make your own] will give you a good reference point when you are designing your new shirts.
You can see how those colours will look against shirts of different colours.
Note that the “display” colours are brighter for “Stickers”. This is because these colours are printed onto a gloss-white background, as opposed to t-shirts which are a low-res matt background.