A lot of image-heavy sites use Skeleton Screens to avoid showing a loading icon to their users. Pinterest takes it a step further and calculates the dominant colour of each image and use that as a placeholder. This snippet will allow you to achieve a somewhat similar visual effect.
If you are having trouble with the pen, try the archived copy on GitHub
Skeleton Screens for Images Snippet
See the Pen Dominant Color Lazy Loading by ComeOnCreative (@ComeonCreative) on CodePen.0