VirtualScroll ion-img background color

When using virtualscroll with ion-img like so:

<ion-list [virtualScroll]="posts">
<ion-item *virtualItem="let post" approxItemWidth="20px" approxItemHeight="20px">
<ion-img [src]="post.IMAGE"></ion-img>
</ion-item>
</ion-list>

The images gets loaded with a grey background until loaded and faded in. How can this background color be changed to another color, or ideally transparent? Where is it defined, can it be overruled?

Thx!