Develop the character's physical characteristics
Sure, the fact that your protagonist has blonde hair may not impact the plot. But it may color how other characters respond to them. And it can only benefit you, as the author, to have a detailed image of them in your mind as you write your story.
Early in your character development, put a bit of time into sketching out your protagonist's physical features, including their...
— Appearance: What do they look like? Does their appearance play a role in the story?
— Voice: What do they sound like? Do they speak with an accent, or an unusual cadence? Does their voice appear to “match” their appearance?
Sure, the fact that your protagonist has blonde hair may not impact the plot. But it may color how other characters respond to them. And it can only benefit you, as the author, to have a detailed image of them in your mind as you write your story.
Early in your character development, put a bit of time into sketching out your protagonist's physical features, including their...
— Appearance: What do they look like? Does their appearance play a role in the story?
— Voice: What do they sound like? Do they speak with an accent, or an unusual cadence? Does their voice appear to “match” their appearance?