Seeing different colours on different devices
When painting using the reference photo, it is best to have the image on your tablet or computer as often the colours on a printout are not very accurate and sometimes detail can be hard to see.
Apple screens are always truest to life, with other makes of screen usually appearing more blue. But whatever screen you view on, the key is to be consistent and use the same device to view the reference photo throughout the tutorial. If there's a big difference in colour between your tablet and computer then you may want to watch the videos and view the reference photo on the same device for consistency. See this page for more advice on how to use the tutorials.