This is by design.

The old bitmap icons (2007) took far too many resources, making them use more memory than necessary.
A 16x16 bitmap is terrible in memory and looks really bad when scaled on new monitors.

The new system uses vector style images, making them use far less memory and looks wonderful at any scale.

Therefore, there will be a brand new set of vector clip art for you to use in the coming weeks. This also means you can tint any of the folder icons, flag markers, resource icons to any colour you wish, and use the new vector art on the Noteboard. Exciting things this way comes.

I believe this to be a future proof solution for many years to come.