To your eyes it is correct and that is fine .
But I doubt there is anyone alive today who has seen Midland loco straight out of the works and could define its colour. Colour perception and memory is poor. Light conditions, weathering and fading of colour make a huge difference.
I had a friend, a professional mountain artist, who couldn't always finish paintings on the hill. She made colour swatches before she started so that she had references to work from. Sadly she is no longer with us but I do own two of her paintings.
Nick