Just in case you have seen similar issue, I have found a solution to it.
In the file express.visualelementsmanifest.xml inside C:\Program Files (x86)\Garmin\Express, there is a line overriding the icon colour in the start menu (i.e. BackgroundColor="#3396cf"). Once you remove that line of code, the icon will approve, and the colour of the tite will follow system default.