## 3 Results
### pH-Response of Samples Films  
Table 2 provides a detailed illustration of the color transformations observed in film samples (P.P, P.P-PVA, and P.P-PVA-AgNP) when immersed in buffer solutions at different \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Color Parameters**} \\ \hline
**pH Value** & \(\mathbf{L^{*}}\) & \(\mathbf{a^{*}}\) & \(\mathbf{b^{*}}\) & \(\mathbf{\Delta E}\) \\ \hline pH 1.0 & 17.8 & 41.7 & \(-\)5.2 & 86.4 \\ pH 2.0 & 24.2 & 34.1 & \(-\)5.8 & 77.1 \\ pH 3.0 & 30.1 & 15.8 & 0.5 & 65.0 \\ pH 4.0 & 42.7 & 5.8 & 2.4 & 50.9 \\ pH 5.0 & 38.6 & 2.9 & 5.3 & 55.1 \\ pH 6.0 & 3.4 & 13.8 & 2.8 & 90.8 \\ pH 7.0 & 1.2 & 4.2 & \(-\)12.0 & 92.0 \\ pH 8.0 & 4.7 & \(-\)8.7 & \(-\)7.4 & 88.4 \\ pH 9.0 & 46.7 & \(-\)1.6 & 14.9 & 49.7 \\ pH 10.0 & 30.1 & \(-\)1.9 & 20.6 & 67.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Color parameters (L\({}^{*}\), a\({}^{*}\), b\({}^{*}\)) of the anthocyanin extract in buffer solutions with pH values ranging from 1.0 to 10.0.  
pH values (1, 4, 7, and 10), along with their specific color parameters (L*, a*, b*) and total color difference (\(\Delta\)E). Initially, the films exhibited predominantly red colors in highly acidic conditions (pH 1). Gradually increasing the pH towards more neutral conditions (pH 4 and 7), the films transitioned through pink and brown shades, ultimately developing a green coloration when immersed in a basic solution (pH 10). Quantitative analysis indicates that the a* parameter consistently decreases with increasing pH, visually confirming the transition from red to green. This phenomenon is particularly pronounced in the film containing silver nanoparticles (PP-PVA-AgNP), which experienced a significant decrease from 36.1 to \(-\)0.1, highlighting remarkable sensitivity and clear signaling of pH changes. On the other hand, the b* parameter, associated with yellow tones, also shows a considerable increase, particularly in the original P.P film, rising from 3.7 to 17.4, indicating a shift towards more yellowish colors with increasing basicity. However, incorporating PVA introduces an inflection in this trend at higher pH values, an effect positively moderated by the addition of silver nanoparticles. In terms of luminosity (L*), the original P.P films exhibit slightly lower values, indicating overall lower brightness. However, incorporating PVA significantly enhances brightness, particularly in acidic conditions (pH 1-4), reaching values close to 40.1 at pH 7. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Film** & **Moisture Content (\%)** & **pH** & & & **Color Parameters** \\ \hline P.P & 1.10 & & \(\mathbf{L}^{*}\) & \(\mathbf{a}^{*}\) & \(\mathbf{b}^{*}\) & \(\Delta\)E \\  & & 1 & 26.8 & 17.1 & 3.7 & 68.9 \\  & & 4 & 28.6 & 12.9 & 2.4 & 65.8 \\  & & 7 & 30.3 & 10.2 & 11.8 & 65.4 \\  & & 10 & 29.2 & \(-\)1.6 & 17.4 & 67.1 \\ P.P–PVA & 1.58 & & & & \\  & & 1 & 33 & 32.2 & 7.6 & 69.4 \\  & & 4 & 37.5 & 19.5 & 8.9 & 60.4 \\  & & 7 & 40.1 & 13.8 & 14.6 & 57.8 \\  & & 10 & 31.4 & 0.6 & 7.1 & 62.3 \\ P.P–PVA–AgNP & 3.37 & & & & \\  & & 1 & 34.3 & 36.1 & 10.8 & 70.9 \\  & & 4 & 37.8 & 24.3 & 16.1 & 63.8 \\  & & 7 & 37.8 & 12.1 & 16.9 & 60.3 \\  & & 10 & 33.1 & \(-\)0.1 & 13.5 & 62.1 \\ \hline \end{tabular}
\end{table} 
Table 2: Moisture content of each film and their color parameters across a range of buffer pH values. Subsequent incorporation of AgNPs maintains this brightness improvement without any negative impacts, providing additional benefits that preserve the visual clarity of the films. These color changes arise from the pH-dependent equilibria of anthocyanins: red flavylium cations dominate in acid, while blue-green quinoidal bases and yellow chalcones prevail in neutral to basic media. When anthocyanins cap silver nanoparticles, plasmon-chromophore coupling amplifies and stabilizes the corresponding spectral shifts, giving the P.P-PVA-AgNP films a particularly sharp and reversible pH response.