I bet I know. I'll bet you that the original image is CMYK or Lab Color, and that when uploaded to Marketo it's being forced to RGB as web default. If you open the original image in Photoshop and convert it to RGB and upload it again I believe you'll recieve it in the proper color space.
Typically when something is previewed as wildly out of color and much too much satuation/brightness/contrast it comes from CMYK images being viewed in RGB.