They spent all this money making the series but couldn't afford $20 for some hair dye to make David a red-head?
Then there's Jesse as well as David's personalities.
The book of Samuel is a limerick of opposites compared. Eli (the high priest) who never bothered to teach, preach, or even read the Torah....didn't bother to discipline his sons....let people do whatever at the Tabernacle. Then there's Samuel willing and obedient to learn and do what God says.
Meaning
There was ONLY one way for David to learn the LAW....because his father Jesse must have had a Torah scroll. All of David's Psalms reflect being intimately familiar with the Law and Joshua. He knew it just as well as his own name. When David was stressed and under duress he clung tighter to the LAW than when things were going well.
David, as a very small child, was a shepherd....and shepherding requires talking or singing constantly to the sheep. Jesse would not have cared one bit about David's lyre...probably encouraged it's use.
David was likely teased unmercifully about his "tough guy" routine while being so small while his brothers were so big. (Where is the stinking farm and crops?)
Also I've noticed that the movie completely ignores EVERY detail of living a Caste based lifestyle. Sure, David's brothers would fight along side of Saul....but to support him being king when they are from the tribe of Judah?
Uhhhh....NO. it was in their best interests to be the brother, cousin, nephew of the king. Judah is to rule....that's a key lesson from Genesis and the rest of the Torah.