Which hair color formula would be used to cancel out yellow undertones in blonde hair?

To effectively cancel out yellow undertones in blonde hair, a violet or purple-based toner is used. This is because colors on the color wheel directly oppose each other will neutralize one another. Yellow is positioned on the warm side of the color wheel, while violet is on the cool side. Therefore, applying a purple-based toner will counteract and neutralize the unwanted yellow tones, resulting in a more balanced and aesthetically pleasing blonde shade.

The choice of violet is particularly effective for blonde hair since the color blonde can often have yellowish hues, and using violet helps to achieve a cooler and more neutral blonde look. This process is commonly utilized in the hair coloring industry to maintain the desired shade and enhance the overall appearance of blonde hair.

In contrast, the other options are not ideal for this purpose. A blue-based toner is typically used to neutralize orange tones rather than yellow. A green-based toner is effective for red tones, and a brown-based toner would add depth or richness but would not address yellow undertones specifically. Thus, the use of a violet or purple-based toner is the most effective choice for canceling out yellow undertones in blonde hair.