Color change in Redbubble show

When I upload a picture in PNG format, e.g. there is a light blue color (RGB 170-224-249) when it will be shown on the public view the light blue has been turned to sort of grey (RGB 159-181-192). This makes that the inages doesn’t have right colors to show for the public. In some cases this effect makes it look like a bit dirty.

Anyone noticed this same problem? And maybe found some solution?

read here

Thanks for your reply. it helped to understand the reason.

Maybe somewhere is some instructions about what color I should use if I want it to result as light blue, or maybe it never will. Actually I should quess, that when printed on white, the colors will be quite near the same as on original file.