Hello Shintori and welcome to the ArtRage forums
Ah, what you are seeing there is the canvas/paper grain interacting with the pastel tool.
All tools in AR interact with the canvas/paper they are used on in much the same way as their real world counterparts do. If you were to magnify real dry media on a toothy paper you will sometimes see small specs of paper still showing.
If you want less tool interaction with the canvas/paper than you are getting by just adjusting the tool’s settings, then you can also change the canvas roughness and grain size to something smoother by opening the Canvas Settings panel: View > Canvas Settings.