Yes, the overlay color for the header image can be changed at ‘Appearance’ > ‘Customize’ > ‘Colors’.
Under the ‘Header’ sub-heading there is the ‘Background Overlay’ setting.
To make it completely transparent so there is no color overlaid, slide the transparency slider all the way to the left until it says “0”.
The transparency slide control is the horizontal control below the color picker. If you are going for zero it doesn’t matter what color you select from the color picker as it will be completely clear when the transparency setting is zero.