A hair-coloring device for coloring hair roots, the device comprising: a) a hair-penetrating shield 220 comprising a tooth array having top 280 and bottom 290 surfaces and having proximal 228 and distal 224 ends and defining mutually perpendicular lateral 260, longitudinal 250 and shield-thickness 270 axes, the tooth array including at least eight closely-spaced teeth such that for a majority of teeth of the tooth array: i) each tooth of the majority includes a main portion 330 and a tapered distal portion 240 for facilitating hair penetration; and ii) for each tooth of the majority, the main portion 330 includes a section having a length of at least 2.5 cm where for most locations along the tooth axis within the section: A) a cross section of the tooth has (i) a substantial triangular shape, the substantial triangle pointing upwards along the shield thickness axis 270 or (ii) an asymmetric width profile along the shield thickness axis 270 such that the tooth cross section, on average, is narrower near the top 248 of the tooth and the tooth cross section, on average, is wider near the bottom 246 of the tooth; B) the tooth cross-section is less than 5 mm^2; and C) the tooth is separated from a laterally neighboring tooth to provide a minimum gap distance 370 that is between 0.3 mm and 1 mm, and b) an aerosol assembly 400 coupled to the hair-penetrating shield, the aerosol assembly including an aerosol outlet elevated above the top surface 280 of the shield, the aerosol assembly configured to dispense a non-viscous hair-coloring agent as a mist in a proximal-distal direction defined by the array of teeth onto the top 280 surface of the shield 220 such that the hair-penetrating shield protects the space beneath the bottom surface from the non-viscous hair-coloring agent. a) a hair-penetrating shield 220 comprising a tooth array having top 280 and bottom 290 surfaces and having proximal 228 and distal 224 ends and defining mutually perpendicular lateral 260, longitudinal 250 and shield-thickness 270 axes, the tooth array including at least eight closely-spaced teeth such that for a majority of teeth of the tooth array: i) each tooth of the majority includes a main portion 330 and a tapered distal portion 240 for facilitating hair penetration; and ii) for each tooth of the majority, the main portion 330 includes a section having a length of at least 2.5 cm where for most locations along the tooth axis within the section: A) a cross section of the tooth has (i) a substantial triangular shape, the substantial triangle pointing upwards along the shield thickness axis 270 or (ii) an asymmetric width profile along the shield thickness axis 270 such that the tooth cross section, on average, is narrower near the top 248 of the tooth and the tooth cross section, on average, is wider near the bottom 246 of the tooth; B) the tooth cross-section is less than 5 mm^2; and C) the tooth is separated from a laterally neighboring tooth to provide a minimum gap distance 370 that is between 0.3 mm and 1 mm, and i) each tooth of the majority includes a main portion 330 and a tapered distal portion 240 for facilitating hair penetration; and ii) for each tooth of the majority, the main portion 330 includes a section having a length of at least 2.5 cm where for most locations along the tooth axis within the section: A) a cross section of the tooth has (i) a substantial triangular shape, the substantial triangle pointing upwards along the shield thickness axis 270 or (ii) an asymmetric width profile along the shield thickness axis 270 such that the tooth cross section, on average, is narrower near the top 248 of the tooth and the tooth cross section, on average, is wider near the bottom 246 of the tooth; B) the tooth cross-section is less than 5 mm^2; and C) the tooth is separated from a laterally neighboring tooth to provide a minimum gap distance 370 that is between 0.3 mm and 1 mm, and A) a cross section of the tooth has (i) a substantial triangular shape, the substantial triangle pointing upwards along the shield thickness axis 270 or (ii) an asymmetric width profile along the shield thickness axis 270 such that the tooth cross section, on average, is narrower near the top 248 of the tooth and the tooth cross section, on average, is wider near the bottom 246 of the tooth; B) the tooth cross-section is less than 5 mm^2; and C) the tooth is separated from a laterally neighboring tooth to provide a minimum gap distance 370 that is between 0.3 mm and 1 mm, and b) an aerosol assembly 400 coupled to the hair-penetrating shield, the aerosol assembly including an aerosol outlet elevated above the top surface 280 of the shield, the aerosol assembly configured to dispense a non-viscous hair-coloring agent as a mist in a proximal-distal direction defined by the array of teeth onto the top 280 surface of the shield 220 such that the hair-penetrating shield protects the space beneath the bottom surface from the non-viscous hair-coloring agent.