Pick the pixel, not a resized average
Choose a local image, then tap or click a pixel. Zoom changes its display size without changing which original pixel is sampled. The loupe shows the neighborhood around the selection. Enter the sampled HEX in the color picker to adjust its channels or opacity.
A worked example
In an image with a red left half and blue right half, sampling inside the left half gives #FF0000 and the right half gives #0000FF.
Before you use the result
Browsers decode images and apply color management. JPEG compression, transparency and color profiles can affect the sampled color. Transparent pixels include an alpha value. The original file is not uploaded.