Beware the effects of incident lighting on colour perception. As a human, you do a lot of processing you're not even aware of to normalise the colours you perceive. Cameras cannot do this (without calibration), so if the incandescent/flourescent/daylight/sunlight mix and intensity is different in the store to your house, you could end up with a very different shade.
It's really interesting. My wife and I have done lots of painting at our house over the past year and we never get exactly what we expected. Most recently, we spent a long time selecting a light gray, which looked very much gray with a group of other grays. Then we painted the first portion of wall, stepped back and both said, "well, that is blue".
I'm guessing you looked at the paint in the shop under artificial lighting (which is more orange - making blues look more grey), then painted it in your house where there is more bluer daylight!
Always buy the extortionately priced test samples. It's worth it!
Matching the appearance of existing paint / colored surfaces is difficult.
You need data on the variation of colour, intensity and reflectance as a function of viewing and illumination angles.
Not something a mobile device can do.
The device described in this paper can:
(note: I am not affiliated; just out of interest)
If you have an app, and a standard color card[1]. then the processing to normalise the image (and therefore the colours) should be doable on a mobile device.
