Makeup Application and Color Theory
The color wheel
Primary colors (red, yellow, blue) mix into secondary colors (orange, green, violet), and those mix into tertiary colors. Complementary colors sit opposite each other and neutralize one another; analogous colors sit next to each other and blend harmoniously. Warm colors (red, orange, yellow) advance and brighten; cool colors (blue, green, violet) recede and shadow. Undertone - the underlying pink, yellow, or neutral cast - differs from surface tone and from the client's Fitzpatrick phototype.
Applying theory to the face
Green cancels redness, peach or orange cancels blue-grey (dark circles, beard shadow), yellow cancels purple, and lavender brightens sallow yellow. Foundation should match along the jawline and be checked in natural light. Lighter shades highlight and bring forward; deeper, cooler shades contour and recede. Face shape informs placement, not a formula.
Sanitation in the kit
Scoop product with a clean spatula onto a palette, use disposable applicators, sharpen pencils, and never dip a used wand, sponge, or brush back into a container. Brushes are cleaned and disinfected between clients; mascara and liquid products that touch the eye are single-use or client-owned. Testers in retail areas are a sanitation hazard, not a demonstration.
Traps: confusing warm/cool undertone with surface color; assuming "hypoallergenic" means allergy-proof; contouring with a warm bronzer on a cool-toned client.
Rule of thumb: cancel with the opposite - pick the color across the wheel from the color you want to hide.