It depends what you call blue as there are many shades of blue, there is also a 3d effect shading which makes it appear blue/grey. It also depends on several other things, graphics card, monitor, background colour of the taskbar, etc. see image 1.
The main thing is not the colour but the functioning of avast, when scanning the avast icon rotates, the various providers (detailed view) Last scanned: and Scanned total: files would be updated as scanning takes place.
What avast processes are running in Task Manager, they begin with ash or asw, see image2 ?