How To Hide The Outline of The Polygon in Altium
It looks like you're making a big polygon, and then using a keepout line within the polygon to define the actual shape you want filled.

Instead of doing that, you can use the function "create polygon from free primitives" to make the polygon the actual circular shape you want. (i.e. draw a circle, convert this to a polygon, change the polygon properties as desired) Then the outlines of the polygon will be on the edges of the filled area, and won't distract from viewing the rest of the design.