Sidebar App Icons in different colours

One of our clients reports the following: on the sidebar, some icons display in grey as expected, others appear in white. Affects standard teams apps also as custom apps.

https://www.directupload.net/file/d/6688/zmcxgdif_png.htm 

Only appears while using Teams Client on a VMware VDI.

Any ideas for reason and/or soultion?

Thanks!