Koleston Perfect 4/0 Medium brown. However, very dark brown to me. There are many more black painted 4/0.
If your hair is dark?
4/0 hair with a hair dye would be very dark brown.
Mixing Recommendation
Combine with Koleston Perfect Crème Developer for outstanding, high-density results. Koleston Perfect Base & Koleston Perfect Crème Developer (1:1). Special Blonde shades ratio (1:2).
MIXING RATIO:
3 levels of lift: 1 part Koleston Perfect, 1 part Koleston Perfect Crème Developer 12%
2 levels of lift: 1 part Koleston Perfect, 1 part Koleston Perfect Crème Developer 9%
1 level of lift/Coverage of gray/white same depth or darker: 1 part Koleston Perfect, 1 part Koleston Perfect Crème Developer 6%
Special Blonde: 1 part Koleston Perfect, 2 parts Koleston Perfect Crème Developer 9% or 12%
SAME DEPTH OR DARKENING:
Full-head color, first-time application: Dampen the hair. Distribute the color from roots to ends and evenly comb through.
Development time: – HEAT: 30–40 min / + HEAT*: 15–25 min
LIGHTENING:
Full-head, first-time application, mid-lengths and ends: Comb through on mid-lengths and ends.
Development time: – HEAT: 20 min / + HEAT*: 20 min
Root area: Apply color to the roots.
Development time: – HEAT: 30–40 min / + HEAT*: 15–25 min
Application
Perfect for all coloring techniques
SAME DEPTH OR DARKENING:
Full-head color, first-time application: Dampen the hair. Distribute the color from roots to ends and evenly comb through.
Development time: – HEAT: 30–40 min / + HEAT*: 15–25 min
LIGHTENING:
Full-head, first-time application, mid-lengths and ends: Comb through on mid-lengths and ends.
Development time: – HEAT: 20 min / + HEAT*: 20 min
Root area: Apply color to the roots.
Development time: – HEAT: 30–40 min / + HEAT*: 15–25 min
wella.com/koleston
If your hair is light 4/0, you would have medium brown paint. 
