Hi, thanks for using our theme.
If you want to remove the image zoom effect only:
Please login wp-admin, go to Aside / General Settings / Custom Css
Paste the style code to Custom Css:

.brick-with-img .brick-hover:hover ~ .brick-content img,
.isotope-liquid-list .hover-effect .brick-hover:hover img {
   -webkit-transform: scale(1);
   -moz-transform: scale(1);
   -o-transform: scale(1);
   -ms-transform: scale(1);
   transform: scale(1);
   -ms-filter: "progid: DXImageTransform.Microsoft.Alpha(Opacity=100)"; filter: alpha(opacity=100); opacity: 1;
}

Also is it possible to change the colour of the ‘dimming’ effect when mousing over a portfolio item (it’s currently grey

You could edit the post, change the featured color in Post Option panel.

Best