How can I change the default blue image on Visual Composer Grid?

I’d like to have a relevant fallback image in case someone forgets to set a featured image for the posts the grid is displaying.

I’ve tried everything, but can’t work it out. If I select ‘use featured image’ and the post in question doesn’t have one, I get a blue image, vc_gitem_image.png.

I’ve tried replacing the image with my chosen image and it won’t show up, I’ve tried php snippets, css. Nothing. Please help.

Did you get this resolved somehow?

I’ve manage to replace image using .htaccess redirection.
add something like this to your .htaccess file in wp root folder, under # END WordPress

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^wp-content/plugins/js_composer/assets/vc/vc_gitem_image.png$ wp-content/themes/your-theme-folder/image-you-want-to-use.png