Blonde changes lightness; brown gives you more control over depth
Going blonde usually creates the larger contrast change because it removes visual weight from the hair and can make brows, eyes, and facial features stand out differently. Brown is not one dark endpoint: caramel can keep brightness, chestnut adds warmth, ash brown reduces red reflection, and espresso adds depth. Compare a medium blonde and medium brown before testing extremes so the choice is not distorted by platinum or near-black intensity.
