What factors will change the final copper-blonde color I get?

The final shade is not guaranteed because it results from a chemical reaction between the dye and your unique hair. The most significant factor is your starting base color. On light blonde or pre-lightened hair, the warm copper tones will appear vibrant and true-to-tone. On darker blonde or light brown hair, the result will be a deeper, more subdued copper-blonde. On virgin (never colored) medium to dark brown hair, the dye may not lift enough to reach a true copper-blonde without pre-lightening.

Previous dye history matters greatly. Coloring over existing permanent color, especially dark shades, can lead to uneven results or a muddy tone. The condition of your hair also plays a role; highly porous, damaged hair absorbs color quickly and can sometimes grab too much warmth or appear patchy. Your hair's natural undertones (warm/yellow or cool/ash) will also mix with the dye's pigments, subtly shifting the final result.