Color filter flags have tiny bit of color (single pixel maybe) on the filmstrip panel.

Using latest windows 10 and lightroom cc classic, the color labels are hard to see.

I think it is because its started on a 4k monitor with the the "recommended 150%" scaling on display properties, if I set the scale to 100% and restart they are normal.

If I restart the PC and initially start lightroom on a lower resolution monitor it is also normal, I can then drag it to the 4k monitor and it remains normal.

Please post a screen-capture of the issue.

Also, please let us know the exact versions of your OS and Lightroom.

Please include a screen shot of the LR Classic window showing what you are seeing.

To my knowledge there is no Color filter Flag. There is a Color Label. The Color Lable is just a boarder around the actual image in both the Grid view and the filmstrip.