If your images look desaturated, washed out, or simply don't match the files on your monitor, they may not be in the recommended Color Profile.
For consistent color display across all devices, you should ensure that your files are in sRGB. sRGB is the magical formula that ensures all browsers and mobile browser can read and display your colors correctly. If your images appear to be washed out, discolored, or have a greenish hue when downloaded then they are likely not in the correct color profile. You will need to convert these files to sRGB and then upload the new files to Pixieset.
If you are using the Pixieset Lightroom Plugin, you can check your Color Space in your Settings: