Yes, this is a serious question that I have received a few times every year.
I don't think it stems from people not being able to tell the difference between grey and blue, I believe it's
to do with the poor quality of some photos that some companies take for their aftermarket stereo surrounds.
It's very easy to take a photo of a grey interior and for it to come out looking blue through
either unintentional manipulation of the photo to make it lighter, brighter or to fix the contrast.
Just look at your interior. The blue isn't subtle, it's very blue.
This photo below shows the best colour difference that I could find.
Look at the blue stereo compared to the grey around it.
If you have a 700cc smart fortwo, you will have a grey interior unless someone swapped it all over.
Look at the interior door plastic on the closest door, underside of the dash, centre console. That's blue.
Even in this photo however, the speedo cowl and furthest door plastic could be mistaken for grey.
Just use your eyes in plain daylight and the colour will be obvious. Thanks to Fotios K for the photo.
Look at your interior colour and see if it's blue or grey. Look at the description of the plastic part or
stereo surround you want to buy. Ignore the photo. If it says it's the same colour as your interior,
take it as read that it is right. If they are wrong, send it back for a refund.