Momma and Dad have made it quite clear to Byron that they disapprove of the "conk" hairstyle popular among young black youth at that time.  Momma says,

"You've known all along how we feel about putting those chemicals in your hair to straighten it, but you...went and did it anyway...did those chemicals give you better-looking hair than me and your daddy and God gave you?" (Chapter 7)

Momma and Dad do not like the "conk" because in their opinion it looks ridiculous, and the use of strong, corrosive chemicals might be harmful to their son, but the reasons for their dispproval actually go much deeper than just the traditional battle between parents and teens that repeats itself over generations.  A hairstyle like the "conk" is an attempt on the part of Negro youth to look less black, and Momma and Dad want Byron to be happy with who he is.  Byron is always trying to gain acceptance with his peers by being "cool", and through negative behavior; he is never content with just being himself.  Momma and Dad are angry that Byron got "new hair" because he did it in direct defiance of their wishes, and because it is just another in a series of bad choices Byron has made in regards to his behavior.