The blue tint/hue is a camera overlay. It shows which parts of the video are visible or in focus. If you're not actively using this feature, you can hide it by clicking on the icon to the left of the camera timeline, as shown below.
Toonly: Why Does My Toonly Canvas Have A Blue Tint?
Learn why your Toonly canvas has a blue tint — it is caused by the camera overlay from the Pan and Zoom feature — and how to hide it by clicking the icon to the left of the camera timeline.