Alright, thank you for clarifying. I hope I can replicate the bug because it's so rare, but I don't want people to be stuck in the design screen.
As for the screenshot - that is a legitimate bug that's been recorded by many others so far. Sometimes the design you make, even if it matches perfectly, won't be accepted. Has nothing to do with the exact shade of colour ;) It's not very common, but can happen every once in a while! Thankfully this is fixed in the next update.
Don't worry, I never explicitly told the player you don't need the exact shade of a colour to complete a client - it's just something running in the background for the people that don't have the best eyesight and aren't able to see the differences between the shades all that well.