Until I upgraded to Windows 10 whenever I had more than one DO running the icons were different colours in the taskbar. Now they are all yellow and I cannot find a way in the preferences to have them all different. I usually have several DO's running on my monitors and I found the various colours useful. Help please!!
If you have the taskbar set to group all windows into a single icon per program, there's only one icon on the main taskbar and it's always the same color.
The icons for individual windows can change color to indicate state (source, dest, off, or dual), but you'll only see those if you hover over the group icon to show individual windows, or if you turn off grouping on the taskbar.
I think we are at crossed purposes. I have uploaded a small screen grab of part of my taskbar. As you can see there are several yellow light bulbs. These used to be different colours but they are now all the same. The 1st was always yellow but the subsequent ones were different colours.
By default the icon will be yellow, red, blue or and sometimes grey. It indicates the source/destination/dual state of the Lister. There's no other meaning besides that.
What Jon says just above is true when the taskbar is not grouping.
From your screenshot, your taskbar looks like it is in a strange mode, which looks like a hybrid of grouping and non-grouping modes. It's not grouping (it has multiple icons for single applications, both Opus and Thunderbird), but it's only showing icons and not labels.
Normally, the Windows taskbar will show labels when it is not grouping, and hide labels when it is grouping.
It's possible your taskbar/shell are confused about which windows belong to which apps. Sometimes unpinning and re-pinning an application can help there.
Are you running anything that modifies how the taskbar behaves?
Thank you for jogging an old mans memory. I do use task bar tweaks and one of the settings had changed without my knowledge (Senior moment probably). I have reset it and now my icons have different colours. Your comment work my brain cells. I try to make my desktop as simple as possible like it was with the Amiga 1200 when I first used DO. Thanks for your help and I am now a "happy bunny" again.