I think that you still can't use it. The following is from this World Cube Association regulations page
"3d) Puzzles must either have coloured stickers, coloured tiles, textures or painted colours.
3h) No modifications are allowed that enhance the basic concept of a puzzle. Some examples of enhancing the basic concept are: new moves are possible, normal moves are impossible, more pieces are visible, colours on the backside of the puzzle are visible, moves are done automatically, more or other solved states."
I think because of 3h, stickerless cubes can't be used. This is because, for example, when you turn the right layer 45 degrees, looking from the left side, you can see both colors of the corner on top. Also, the cube would violate 3d because it doesn't have stickers, tiles, textures, or painted colors; the plastic is colored.