I had a client last week, have done her 4 times now, she just has a Colorance Demi colour but always about 5-7 months apart. She is quite challenging for such a simple service. First time insisted on seeing the manufacturer instructions, and last time was convinced I hadn't mixed up correct colour as she thought it looked different so I had to physically show her the tube!
At the end she asked to see the shade chart again and then got her phone out and took a pic of the shade chart and pic of the swatch we had used! I have no idea what she intends to do with the information, I'm guessing she will try and buy on line but she would have no idea what developer to buy to go with it but we go through the same rigmarole every time and she is always pleased but I'm worn out with all her questions, it's like I'm being interrogated!