Hi,
As you can see at the following video: Screen capture - a6ea0d224b83d5fbe382e4e3b9323122 - Gyazo,
when i upload an image as icon of the app, it becomes blue… i’ve tried with several logos and always the same happens… even if the background is white or clear/transparent, why is that and how to fix it?
Try changing your image to a jpeg file first. 
PNG files allow for transparent backgrounds if the image was designed what way. What you think is a white background is actually a transparent background, meaning the background color shows through the transparent parts. You need an image with a solid opaque background.
Thanks, i almost made it work using .png file format, and using solid black as background, as unfortunately the transparent becomes blue and the result is not the same as other’s 
If the browser is not entirely black, then my favicon appears “square”, while other sites usually use it round…
What’s the best way to get it round and that out of the circle it’s “transparent”? Glide transforms my transparent backgrounds into blue…
Yes, your icon essentially doesn’t have a background (it’s transparent). If you convert it to JPEG, it will force you to add a background to show the difference. Actually, you can keep using PNG as long as you add color to the background.
You should use a PNG file with a round background for your icon. However, keep in mind that this doesn’t always guarantee transparency. Some browsers or devices may convert the transparent areas into a square format by filling in the background with a specific color. This can lead to your favicon not appearing round on certain platforms.
i tried, but then the same icon is used at the app with blue corners, as you can see at my screenshots.
The square shape is the default style. My suggestion is to keep using the square format. If your plan supports custom CSS, you can modify it to a circular shape, but this won’t apply to all icons.
My main concern is the favicon, glideapps and upwork sites for example display their round favicon everywhere without issues… glide should allow the same to its users
I thought you were talking about the favicon in the browser tab.
However, if you meant the icon/logo on the dashboard and the published app, I believe Glide applies a rounded square shape. Unfortunately, I don’t see any setting to make it a perfect circle. Sorry I can’t help with that.
