Your image files are likely saved with the “Adobe RGB” color profile or something similar, which can lead to washed-out colors in some circumstances, particularly on the web. This is not ArtBinder-specific. If you re-save the images using the sRGB color profile, then it will look as you'd expect in ArtBinder. This is a somewhat older article, but the explanation and methods it recommends are still valid: https://om4.com.au/client/preparing-images-color-profiles-srgb-adobe-rgb/
You will see that the image file saved using the sRGB color profile retains a brighter, more accurate color palette.
For more assistance, please email your Client Success Manager, or email firstname.lastname@example.org.