To determine how much more blue paint Juanita needs, we need to subtract the amount of blue paint she currently has from the amount she needs.
She needs \( \frac{7}{8} \) gallon of blue paint and has \( \frac{5}{8} \) gallon.
So, we subtract:
\[ \frac{7}{8} - \frac{5}{8} = \frac{7 - 5}{8} = \frac{2}{8} \]
We can simplify \( \frac{2}{8} \):
\[ \frac{2}{8} = \frac{1}{4} \]
However, among the response options provided, it seems that \( \frac{2}{8} \) was listed. The answer is:
\[ \frac{2}{8} \]