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Thank you sooo very much

Hi. I'm new to NG, I mean I used to use it a lot to watch art and play games but I started submitting my own art just lately.
So my question is: How do you guys get so good with shadowing? I like painting portraits but I just can't understand how to get to the perfect shadowing on my paintings.
Also I don't think I'm color blind but I get confused with the flow of the color lets say from dark color to bright I get confused on the way...

So do you people have some kind of advise? some training you are familiar with that can help?
PLZ PLZ
Thank you.